LIBRARY 

OK   THE 

University  of  California. 


GIFT  OF^ 


(AMlLsir 

Class    -XlA  7, 


Bg  Captmn  Hcnrg  l^aglor 


PubUstteft  bg  tfie  Author 

S20  Qatterg  Street 

1904 


Entered  according  to  Act  of  Congress,  in  the  year  1904, 

By  Henry  Taylok, 

In  the  office  of  the  Librarian  of  Congress,  at  Washington,  D.  C. 


PRESS  OF 

Walter  N.  Brunt 
10^-104  Second  Street, 
San  Francisco,  Cal. 


MARINER'S  COMPASS. 


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PREFACE. 

This  book  is  devoted  entirely  to  the  subject  of  Navigation,  Nau- 
tical Astronomy  and  Compass  Adjustment,  the  object  being  so  to 
simplify  the  problems  involved,  that  no  matter  how  limited  a  per- 
son's education,  he  may  be  brought  from  comparative  ignorance  to 
a  high  degree  of  efficiency  as  a  navigator,  the  only  requirement  be- 
ing that  the  student  must  be  able  to  read.  There  is  almost  an  en- 
tire absence  of  algebraical  signs. 

The  first  section,  or  opening  part,  is  devoted  to  the  first  four 
rules  of  common  arithmetic.  This  section  is  written  in  the  sim- 
plest language  so  that  any  one  having  but  a  slight  knowledge  of 
English  can  understand,  words  of  one  syllable  being  used  in  pref- 
erence to  longer  words  wherever  practicable,  but  as  the  student 
advances,  better  language  is  introduced,  yet  simplicity  is  never 
lost  sight  of  throughout  the  work. 

The  arrangement  is  such  that  any  part  of  the  work  may  be  re- 
ferred to  with  the  greatest  ease,  and  any  desired  problem  found 
in  a  very  short  space  of  time.  This  is  important,  as  the  book  is 
not  only  intended  for  beginners,  but  also  as  a  work  of  reference 
for  those  that  may  have  become  "rusty." 

Special  attention  has  been  given  to  the  requirements  of  the  mod- 
ern navigator,  whereby  he  can  obtain  the  ship's  position,  at  any 
time  of  the  day  or  night,  by  single  and  double  altitudes  of  the  sun, 
stars  and  planets,  but  all  problems  relating  to  the  moon  have  been 
entirely  omitted,  as  they  are  not  reliable,  and  are  therefore  obso- 
lete. 

The  part  relating  to  the  finding  of  the  deviation  of  the  compass 
will  be  found  to  fit  any  case,  no  matter  what  the  class  of  vessel. 
This  section  is  important,  owing  to  the  use  of  iron  and  steel  in  the 
construction  of  modern  vessels.  This  part  also  contains  a  de- 
scription of  the  different  kinds  of  Pelorus  and  other  instruments 
used  in  the  taking  of  bearings,  and  azimuths,  with  rules  for  using 
the  same,  written  in  very  plain  language, — very  necessary  knowl- 
edge for  the  bridge  officer. 

Chart-work  and  coast  navigation  has  been  thoroughly  gone  over, 
and  many  matters  connected  with  the  same,  not  generally  known 
to  seamen,  have  been  introduced,  especially  those  matters  relating 
to  the  proper  application  and  use  of  deviation  when  taking  bear- 
ings and  finding  the  course  to  steer. 


VI  Preface 


Tides,  and  the  time  of  their  occurrence,  are  also  given,  with  re- 
ductions to  soundings, — very  useful  in  finding  the  depth  of  water 
when  crossing  a  shallow  bar. 

Compass — Adjustment. — This  difficult  subject  is  given  in  an  en- 
tirely different  manner  from  that  generally  found  in  books  of  this 
description,  all  calculations  being  worked  by  addition,  subtraction, 
multiplication  and  division.  This  part  is  illustrated  by  colored 
diagrams.  By  a  very  moderate  amount  of  study  any  navigator 
should  be  able  to  compensate  the  vessel's  compasses  himself. 

The  work,  so  far  as  practicable,  is  original  throughout,  and 
purely  American,  with  special  references  to  the  numerous  publica- 
tions issued  by  the  United  States  Hydrographic  Office  for  the 
benefit  of  navigators.  This  idea,  it  is  to  be  hoped,  will  be  duly  appre- 
ciated, as  there  are  so  many  seamen,  at  the  present  date  of  writing, 
who  are  totally  ignorant  of  the  existence  of  these  useful  publica- 
tions, and  of  the  many  advantages  to  be  derived  from  studying 
them  in  preference  to  foreign  works. 

Every  problem  is  fully  illustrated,  and  numerous  examples  are 
given  for  practice. 

The  author  feels  assured  that  the  book  will  fill  a  long-felt  want, 
for  it  is  the  first  of  its  kind  ever  published  in  the  United  States. 


ORDER    OF    STUDY. 

Take  the  first  part  of  the  book  as  far  as  "Day's  Work,"  then  fol- 
low the  list: 

Latitude  by  Meridian  Altitude  of  the  Sun. 
Mercator  Sailing. 
Amplitude. 

Longitude  by  Chronometer   (Sun). 
NMien  these  are  thoroughly  understood,  the  student  may  study 
any  part  of  the  book  that  he  prefers. 


TABLE    OF  CONTENTS. 


DIVISION  1. 

Page. 

Common   Addition    1 

Common  Subtraction 1 

Common  Multiplication 2 

Multiplication  Tables 3 

Common  Division '^ 

Decimals 9 

Addition — Degrees— Minutes — Seconds   14 

Subtraction — Degrees — Minutes — Seconds 15 

Multiplication — Degrees — Minutes — Seconds    15 

Division  Degrees — Minutes — Seconds 16 

Logarithmic  indices I'i' 

To  correct  Compass  Course  in  points 18 

To  correct  Compass  Course  in  degrees 20 

The  Day's  Work 22 


DIVISION  2. 

The  Sailings -±-t 

Use  of  Table  42 — Logarithms  of  Numbers 41 

Use  of  Table  44 — Sines,  Tangents,  etc- 45 

Mercator  Sailing 46 

Parallel  Sailing 51 

Mercator  Sailing  by  Inspection 52 

Difference  of  Longitude  by  Parallel  Sailing 53 

Middle  Latitude  Sailing 54 

Great  Circle  Sailing 57 


DIVISION  3. 

Latitude  by  Meridian  Altitude  of  the  Sun 59 

Caution  to  the  Eising  Generation  of  Navigators 66 

Special  Table  to  correct  Altitude 67 

Latitude  by  Meridian  Altitude  of  the  Sun  below  the  Pole 71 


Table  of  Contents. 


Page. 

Latitude  by  Meridian  Altitude  of  a  Fixed  Star "ii 

Rule  to  find  the  Time  of  Meridian  Passage  of  a  Fixed  Star 74 

Rule  to  find  what  star  is  approaching  the  Meridian 75 

Rule  to  compute  the  Meridian  Altitude  of  a  fixed  star 75 

Latitude  by  Meridian  Altitude  of  a  planet 77 

To  correct  the  Planet's  Declination 78 

Latitude  by  Pole  Star 81 


DIVISION  4. 

Latitude  by  Ex-Meridian  Altitude  of  the  Sun,  Epitome  method.  87 

Towson's  method 88 

Remarks  on  the  method  of  finding  the  Latitude  by  Ex-Meridian 

Altitude 95 

Latitude  by  Ex-Meridian  Altitude  of  a  Star   96 

Latitude  by  Ex-Meridian  Altitude  of  a  Planet 97 


DIVISION  5. 

Longitude  by  Chronometer 100 

To  correct  the  Chronometer  Time 101 

How  to  state  Astronomically  the  Time  shown  by  a  chronometer.  110 

To  convert  Civil  Time  to  Astronomical  Time Ill 

Rule  to  correct  a  Log  Sine,  Tangent  and  Secant  to  seconds.  . .  .115 

To  find  the  correct  Latitude  to  work  the  sight 116 

The  Modern  Method  of  working  an  A.  M.  sight 124 

Remarks  on  Careless  Navigation 133 


DIVISION  6. 

Longitude  by  Fixed  Stars 135 

Longitude  by  Planet 138 

Remarks  in  regard  to  Star  and  Planet  observations  when  taken 

to  find  the  longitude 1-11 

What  to  do  when  crossing  the  Meridian  of  180  degrees  and 

other  matters  relating  to  the  change  of  time 142 

Little  pointers,  which,  although  not  relating  to  the  crossing  of 

the  180°  of  longitude,  still  have  considerable  bearing  on  it. .  144 


Table  of  Contents. 


Page. 

To  set  the  wheelhouse  clock  so  that  it  will  indicate  approxi- 
mately 12  hours  when  the  Meridian  Altitude  js  observed.  .144 
To  find  the  length  of  a  passage  of  an  Ocean  Greyhound 145 


DIVISION  7. 

Sumner's  Method 147 

Latitude  and  Longitude  by  Double  Altitudes 150 

Chart  illustrating  the  same 151 

Eemarks  on  the  Double  Altitude  problem 153 

Johnson's  Method  156 

The  Stars  and  how  to  find  them 165 

Latitude  and  Longitude  by  Double  Altitude  of  Stars 169 

Chart  illustrating  same 178 


DIVISION  8. 

Deviation  of  the  Compass 173 

The  Amplitude — Epitome  Method 173 

Short  Method  of  Amplitude  by  Table  39  Bowditch  Epitome 175 

Short  Method  of  working  Amplitudes  by  the  American  Azimuth 

tables 177 

The  Altitude  Azimuth 180 

Time  Azimuths 186 

Method  of  Setting  the  Watch  to  Apparent  Time  Sufficiently 

near  to  work  the  Time  Azimuth 187 

To  find  the  Apparent  Time  at  ship  when  there  is  no  chronome- 
ter on  board 189 

Time  Azimuths  by  Stars  or  Planets 191 

Napier's  Diagram 194 

Remarks  on  the  finding  of  the  deviation  by  Star  Azimuths.  . .  .207 

Eange  Bearings 210 

Reciprocal  bearings 211 

Instruments  used  on  board  of  ships  for  taking  bearings 212 

The  Pelorus 213 

Methods  of  using  the  Pelorus 214 

To  use  Field's  Pelorus 215 

The  Shadow  Pin 215 

Good  form  for  Recording  the  Deviations 217 


Table  of  Contents. 


DIVISION  9. 

Page. 

Chart  Work 218 

The  Parallel  Euler 218 

Field's  Euler 218 

The  Transparent  Protractor 219 

The  Three- Armed  Protractor 219 

Dividers 221 

The  Gnomonic  Chart 221 

The  Polyconic  Chart 221 

Mercators    Chart   221 

To  know  if  it  is  a  TTue  or  Magnetic  Chart 222 

Variation  and  Dip  Charts 222 

Pilot  Charts 223 

To  find  the  course  between  two  places  on  a  chart 225 

To  find  the  distance  on  a  Mercators  Chart 225 

Ship's  position  by  cross  bearings 227 

Ship's  position  by  two  bearings  of  one  point 227 

Chart  illustrating  the  same 226 

Ship's  position  by  four  point  bearings  or  double  the  angle,  with 

chart  illustrating  the  same 228 

Current  Sailing 229 

Diagram  illustrating  the  same 230 

To  find  the  compass  course  to  steer  to  make  a  Magnetic  Course 

taken  from  a  chart 231 

Deviation   Card   235 

Remarks  relating  to  the  chart  questions  and  other  matters  in 

regard  to  Coast  Navigation 243 

Listening  for  a  signal  during  a  fog 245 

DIVISION  10. 

The  Tides 247 

Rule  to  find  the  time  of  high  water  by  moans  of  tlio  American 

Tide  Tables  248 

Use  of  the  Tide  Tables  when  taking  soundings  with  the  lead.  .252 


DIVISION  11. 

The  Sextant 255 

To  select  a  good  Sextant 255 


Table  of  ConteiNts. 


Page. 

Color  Shades 2^6 

Bad  Shade  Glasses 256 

Care  of  a  good  Sextant 257 

To  read  the  Sextant 258 

Adjustment  of  the  Sextant 259 

To  find  the  Index  Error 261 

To  Measure  the  Altitude  of  the  Sun 262 

A  Lead  Line 262 

To  cast  the  Deep  Sea  Lead  from  a  Sailing  Ship 264 

Thompson's  Sounding  Machine 264 

The  Log  and  Log  Glass 266 

To  test  a  patent  log  to  see  if  it  registers  correctly 267 

Short  and  handy  rule  to  measure  the  Log  Line 268 

To  mark  the  Log  Line 268 

Definitions 271 


DIVISION  12. 

Keeping  the  Chief  Officer's  Log  Bool-: 284 

DIVISION  13. 

The  Official  Log  Book 288 

The  Meteorological  Log  or  Weather  Report 289 

The   Chronometer   298 

Caution  in  Handling 299 

Care  on  Board 299 

More  than  one  chronometer  necessary 301 

Winding  the  Chronometer 301 

Eating  the  Chronometer 303 

What  to  do  if  the  Chronometer  should  break  down 305 

DIVISION  14. 

Mariner's  Compass — 

Early  History   307 

The  Lubber  Line 308 

Purchasing  a  Compass 309 


Table  of  Contents. 


Page. 

Parsimonious  Owners .' 310 

Caution  in  regard  to  placing  a  compass  and  some  incidents  re- 
lating to  the  same 311 

Bad  position  to  be  avoided 313 

Magnetism 315 

Chance  for  argument 317 

First  law  of  Magnetism 317 

Magnetism  in  an  iron  ship 317 

Magnetism  contained  in  iron  lying  horizontal 330 

Explanation   of   colored   diagrams 321 

Sorting  out  the  Deviation 325 

Quadrantal  Deviation   327 

Computation  of  the  Co-efficients 329 

Computing  the  value  of  each  Co-efficient  for  every  point  of  the 

compass 331 

Table  of  Co-efficients 333 

Placing  the  Compass 333 

Caution  in  placing  Magnets 335 

Size  of  Magnets 335 

Strength  of  Magnets 335 

Care  of  Magnets 336 

Prepare  to  adjust  ship's  Compass  at  sea 336 

Eule  to  find  the  amount  of  Deviation  due  to  vertical  iron 337 

To  adjust 338 

The  Flinder's  Bar 339 

Table  for  correction  of  Quadrantal  error 340 

Eetentive  Magnetism   341 

Further  information  in  regard  to  the  Flinder's  bar 342 

Rule  to  find  the  direction  of  Ship's  head  when  building 343 

The  heeling  error 343 

The  heeling  adjustment 345 

Value  of  heeling  adjustment 346 

Johnson's  Tables 348-349 

Table  for  correcting  Altitude 350 


SIGNS  AND  ABBKEVIATIONS. 

° degrees 

' minutes  of  arc 

" seconds  of  arc 

i' Iioiirs 

™ minutes  of  time 

» seconds  of  time 

-[- plus 

— minus 

A.T.S apparent  time  ship 

Accum.  rate accumulated  rate 

Ast.   T astronomical  time 

Amp amplitude 

Approx approximate 

A.M ante-meridian    (morning) 

Az azimuth 

Alt altitude 

App apparent 

Cor.  decl correct  declination 

Civ.  T civil  time 

Chron.  T chronometer  time 

Co.-lat complement  of  latitude 

Co.-bearing complement  of  bearing 

Diif.   of  lat difference  of  latitude 

Diff.  of  long difference  of  longitude 

Dep departure 

Dist distance 

Decl declination 

D.E dead  reckoning 

Dev deviation 

Equa.   T equation  of  time 

G.M.T Greenwich  mean  time 

G.A.T Greenwich  apparent  time 

H.A hour  angle 

I.E index  error 

Lat latitude 

Long longitude 

L.L lower  limb 

Mer.  Alt meridional  altitude 


Signs  and  Abbrp:viations. 


Mer.  parts meridional  parts 

Mer.    d.   lat meridional  difEerence  of  latitude 

M.T.S mean  time  ship 

]\[.T.G mean  time  Greenwich 

Mid.  lat middle  latitude 

Mer.  Pass meridian  passage 

Mag.  CO magnetic  course 

J^.A nautical  almanac 

Obs.   alt observed  altitude 

Obs.  az observed  azimuth 

Obs.  amp observed    amplitude 

P.D polar  distance 

P.M post  meridian   (afternoon) 

Parlx parallax 

R.A right  ascension 

E.A.  of  Mer right  ascension  of  meridian 

Eef refraction 

S.D semi-diameter 

S.T ship's  time 

Sid.  T sidereal  time 

T.  CO true  course 

T.  Alt true  altitude 

T.  Amp true  amplitude 

T.  Az true  azimuth 

U.L upper  limb 

Var variation 

Z.D zenith  distance 


TAYLORS  MODEETNAVIGATION. 
DIVISION  I. 


ADDITION. 

Add  the  following  numbers : 

2'  6  5  0  5  4  3  7 
15975323 
4267  9  822 
98564327 


183724909 


When  adding  any  number  of  figures,  commence  with  the  column 
to  the  right,  and  whatever  is  over  10,  20,  30,  40,  and  so  on,  mark 
down  under  its  own  column,  carry  1  to  the  next  column  if  the  num- 
ber is  over  10  and  less  than  20,  2  if  over  20  and  less  than  30,  3  if 
over  30  and  less  than  40,  and  4  if  over  40  and  less  than  50,  and  so 
on.  This  rule  will  be  more  easily  understood  if  the  foregoing 
example  is  followed. 


SUBTRACTIOX.— COMMOX  NUMBERS. 


Example. 
From        260785421 
Subtract  173098526 


Ans.  87686895 

When  subtracting  one  number  from  another,  proceed  in  the  fol- 
lowing manner,  as  seen  in  the  example.  Thus,  6  from  1  I  cannot, 
so  I  take  1  from  the  figure  to  the  left  and  place  it  with  the  1,  mak- 
ing 11  of  it ;  now  I  say,  6  from  11  is  5,  so  I  mark  down  the  5 ;  next  I 
say,  2  from  1,  as  I  have  borrowed  1  from  the  2,  making  it  now  1, 
and  as  I  cannot  take  2  from  1,  I  must  borrow  1  from  the  4,  making 
it  3.  and  put  this  1  with  the  other  and  make  it  11  again;  so  I  say,  2 

Taylor's  Mod.  Nav.  1, 


Taylor's  Modern  Navigation. 


from  11  is  9;  next,  as  I  have  borrowed  1  from  the  4,  it  is  now  only 
3,  and  as  I  cannot  take  5  from  3,  I  borrow  1  from  the  5  and  place 
it  with  the  3,  making  13  of  it;  so  I  say,  5  from  13  leaves  8;  next, 
8  from  5,  but  as  I  have  borrowed  1,  it  is  only  4,  so  8  from  14  is  6 ; 
next,  9  from  8,  but  I  have  borrowed  1  here  also,  so  9  from  17  is  8; 
then  as  I  have  borrowed  1  from  the  7,  it  makes  it  6,  so  0  from  6  is  6 ; 
then  3  from  0  I  cannot,  so  I  borrow  1,  and  say,  3  from  10  is  7 ; 
then  7  from  6,  but  here  I  borrowed  1,  and  so  7  from  15  is  8,  and  1 
from  1  leaves  nothing.     The  question  is  then  finished. 

Note. — Any  problem  in  subtraction  may  be  proved  by  adding  the 
two  lower  lines  together.     The  result  will  be  equal  to  the  top  line. 


Examples. 
From       97B042379 
Subtract  429076549 


Ans.         546965830 

From     9000423 
Subtract   2000567 


Ans.      6999856 

MULTIPLICATION  OF  COMMON  NUMBERS. 

When  following  these  examples,  the  student  should  refer  to  the 
multiplication  table  if  he  is  in  doubt. 

Example.  Multiply  69806  by  8 


Ans.  558,448 

The  first  figure,  multiplied  by  8,  gives  48 ;  so  I  mark  down  the  8 
and  hold  on  to  the  4.  Then  I  say,  8  times  0  is  0,  and  add  on  the 
4 ;  so  I  mark  down  the  4.  Next  I  say,  8  times  8  are  64 ;  so  I  mark 
down  the  4  and  hold  on  to  the  6.  Then  8  times  9  are  72,  and  the 
G  makes  it  78 ;  so  I  mark  down  the  8  and  carry  the  7.  Next,  8 
times  6  are  48,  and  the  7  will  give  55. 


Multiplication. 


MULTIPLICATION   TABLE. 


IX  1=  1 

2X   1=  2 

3X  1=  3 

4X  1=  4 

IX  2=  2 

2X  2=  4 

3X  2=  6 

4X  2=  8 

IX  3=  3 

2X  3=  6 

3X  3=  9 

4X  3=12 

IX  i=  4 

2X  4=  8 

3X  4=12 

4X  4=16 

IX  5=  5 

2X  5=10 

3X  5=15 

4X  5=20 

IX   6=r  6 

2X   6=12 

3X  6=18 

4X   6=24 

IX  "=  7 

2X  7=14 

3X  7=21 

4X  7=28 

IX  S=  8 

2X  8=16 

3X  8=24 

4X  8=33 

IX  9=  9 

2X  9=18 

3X  9=27 

4X   9=36 

1X10=10 

2X10=20 

3X10=30 

4X10=40 

1X11=11 

2X11=22 

3X11=33 

4X11=44 

1X13—12 

2X12=24 

3X12=36 

4X12=48 

5X   1=  5 

6X  1=  6 

7X  1=  7 

8X  1=  8 

5X  2=10 

6X  2=12 

7X   2=14 

8X  2=16 

5X   3=15 

6X   3=18 

7X  3=21 

8X  3=24 

5X   4=20 

6X   4=24 

7X  4=28 

8X  4=32 

5X   5=25 

6X  5=30 

7X  5=35 

8X  5=40 

.5X   6=30 

6X  6=36 

7X  6=42 

8X  6=48 

5X   7=35 

6X   7=42 

7X  7=49 

8X  7=56 

5X  8=40 

6X  8=48 

7X  8=56 

8X  8=64 

5X  9=45 

6X  9=54 

7X  9=63 

8X  9=72 

5X10=50 

6X10=60 

7X10=70 

8X10=80 

5X11=55 

6X11=66 

7X11=77 

8X11=88 

5X12=60 

6X12=72 

7X12=84 

8X12=96 

9X   1=     9 

lOX   1=  10 

IIX   1=  11 

12X  1=  12 

OX  2=  18 

lOX  2=  20 

IIX   2=  22 

12X  2=  24 

■9X  3=  27 

lOX  3=  30 

IIX  3=  33 

12X  3=  36 

9X  4=  36 

lOX  4=  40 

IIX  4=  44 

12  X  4=  48 

9X  5=  45 

lOX  5=  50 

IIX   5=  55 

12X  5=  60 

9X   6=  54 

lOX  6=  60 

IIX   6=  66 

12X  6=  72 

9X  7=  63 

lOX  7=  70 

IIX  7=  77 

12X  7=  84 

9X  8=  72 

lOX  8=  80 

IIX  8=  88 

12X  8=  96 

9X  9=  81 

lOX  9=  90 

IIX  9=  99 

12X  9=108 

'9X10=  90 

10X10=100 

11X10=110 

12X10=120 

9X11=  99 

10X11  =  110 

11X11  =  121 

12X11=132 

'.9X12=108 

10X12=120 

11X12=132 

12X12=144 

Taylor's  Modern  Navigation. 


Examples  for  Practice. 
Multiply  297654  by  7 


Ans.      2,083,578 

Multiply  897563  by  5 
5 


Ans.      4,487,815 

Multiply  7098662  by  9 
9 


Ans.      63,887,958 

Multiply  2907654873  by  6 
6 


Ans.     17,445,929,238 


MULTIPLICATION  BY  TWO  FIGURES. 


Multiply  542837  by  25 
25 


2714185 
1085674 


Ans.  13,570,925 

Here  we  multiply  by  two  figures;  so,  on  the  second  line,  when 
placing  the  first  figure  down,  it  must  be  put  under  the  figure  8,  as 
seen  in  the  example;  then  the  two  lines  must  be  added  to  get  the 
proper  answer.  To  read  the  answer,  mark  off,  with  commas,  the 
first  three  figures  to  the  right,  then  the  next  three,  as  seen  above. 
The  answer  will  then  road,  13  million,  570  thousand,  9  hundred, 
and  25. 

Examples  fur  Practice. 

Multiply  926074  by  34 
34 


8704296 

2778222 


Ans.  31,486,516 


Mil  LT I  PLICATION. 


Multiply  9765  by  78 


78120 
68355 


Ans.  761,670 


Multiply  492631  by  92 
92 


985262 
4433679 

Ans.  45,322,052' 


MULTIPLICATION  BY  THREE  FIGURED 

Multiply  419678  by  247 
247 


2937746 
1678712 
839356 


Ans.  103,660.466 

Here  we  multiply  by  three  figures,  and  it  will  be  seen,  in  the  ex- 
ample, that,  each  time  we  multiply,  the  result  is  placed  one  figure 
to  the  left;  then  the  lines  of  figures  are  added  as  before.  The  re- 
sult, in  words,  is  expressed  in  the  following  manner :  103  million, 
660  thousand,  4  hundred,  and  66. 

Examples. 

Multiply  827654  by  725 

725 


4138270 
1655308 
5793578 

Ans.  600,049,150 


Taylor's  Modern  Navigation. 


Multiply  256784  by  623 
623 


770352 
513568 
1540704 

Ans.  159,976,432 


Multiply  5006271  by  987 
987 


35043897 
40050168 
45056439 

Ans.  4,941,189,477 


Multiply     2709832  by  506 
506 


16258992 
135491600 


Ans.  1.371,174,992 

It  will  be  noticed  here  that  there  is  a  0  between  the  5  and  the  6 ; 
so,  when  multiplying  by  the  second  figure,  simply  place  the  0  under 
the  second  figure  from  the  right,  and  proceed  to  multiply  by  the  5, 
as  seen  in  the  example. 

Note. — If  there  were  more  than  one  cipher,  I  would  place  as 
many  ciphers  as  I  was  multiplying  by  under  the  other  figures,  let- 
ting the  first  cipher  come  under  the  second  figure  from  the  right, 
and  then  multiply  as  before. 

Thus,  Multiply  98700234  by  5002 

5002 


197400468 
49350117000 

Ans.  493,698,570,468 

To  prove  any  question  in  multiplication,  simply  divide  the  result 
by  the  number  used  in  multiplying,  and  the  result  will  be  the  first 
row  of  figures. 


Division. 


SHOKT  DIVISION.— COMMON  NUMBERS. 
Example.— Divide  37062786  by  2. 

2)37062786 
Ans.   18,531,393 

Here  we  say,  2  into  3  will  go  once  and  1  over ;  so,  carry  the  1  and 
place  it  before  the  7,  and  we  have  17 ;  then  2  into  17  will  go  8  times 
and  1  over;  this  1  placed  before  the  0  makes  it  10,  and  2  will  go 
into  10  5  times  even.  Then,  2  into  6,  3  times;  2  into  2,  once;  2  into 
7,  3  times  and  1  over;  place  the  1  before  the  8  and  make  18  of  it; 
then  2  into  18  goes  9  times  even,  and  2  into  6,  3  times  even. 

Example.— Divide  726987425  by  4. 

4)726987425 

Ans.     181,746,856,  and  1  over. 

Four  will  go  into  7  once  and  3  over ;  place  the  3  before  the  2 ; 
then  4  into  32,  8  times  even ;  then  4  into  6,  once  and  2  over ;  place 
this  2  before  the  9,  and  say,  4  into  29,  7  times  and  1  over;  place 
this  1  before  the  8,  and  4  into  18  goes  4  times  and  2  over;  then 
4  into  27,  6  times  and  3  over;  then  4  into  34  goes  8  times  and  3 
over;  then  4  into  22,  5  times  and  2  over;  then  4  into  25,  6  times  and 
1  over. 

Examples  for  Practice. 

Divide  956273  by  5.         Ans.  191254,  and  3  over. 

100937  by  7.  14419,  and  4  over. 

1142879  by  8.  142859,  and  7  over. 

To  prove  any  answer  on  this  page,  multiply  the  answer  by  the 
figures  used  when  dividing  and  add  what  is  left  over;  and  the  re- 
sult will  be  the  row  of  figures  divided. 


Taylor's  Modern  Navigation'. 


LONG  DIVISION,  OE  DIVIDING  BY  MORE  THAN  ONE 
FIGURE. 


Example. — Divide  542837  by  25. 

25)542837(21711 
50 


178 
175 


33 
25 

87 

75 

12 

Now  we  divide  by  two  figures,  and  find  that  25  will  go  twice  into 
54,  with  4  as  a  remainder;  so  we  bring  down  the  2  and  then  say, 
25  into  42  once  and  17  over;  so  bring  down  the  8,  and  say,  25  into 
178  will  go  7  times  and  3  over;  then  bring  down  the  3,  and  25  will 
go  into  33  once  and  8  over;  bring  down  the  last  figure,  7,  and  then 
say,  25  into  87  will  go  3  times  and  12  over.  This  ends  the  exam- 
ple, and  the  12  over  is  called  12-25  (twelve  twenty-fifths). 

Example.— Divide  159976432  by  623. 

623)159976432(256784 
1246 


3537 
3115 

4226 
3738 


4884 
4361 


5233 

4984 

2492 
2492 


Decimals. 


In  this  example  we  divide  by  three  figures,  and  find  that  they 
will  go  into  the  first  four  figures  twice  and  353  over;  so  the  7  is 
brought  down,  making  the  number  3537 ;  then  G23  will  go  into  it 
5  times  and  422  over;  so  we  bring  down  the  6  and  divide  again, 
and  continue  in  the  same  manner  until  all  the  figures  are  brought 
down,  when  the  example  will  be  finished.  Tt  will  be  noticed  that 
there  is  no  remainder  here. 

Examples  for  Practice. 
Divide  G00049150  by  725.  Ans.  827,654. 

4941189477  by  987.  5,006,271. 

493698570468  by  5002.  98,700,234. 


DECIMALS. 

A  decimal  is  a  number  which  is  a  tenth,  hundredth,  thousandth, 
etc.,  of  1,  or  unity. 

A  ivhole  number  is  a  number  with  the  decimal  point  placed  to 
the  right ;  thus,  2564. 

A  decimal  7inmher  is  so  called  when  the  dot,  or  decimal  point,  is 
placed  before  it;  thus,  .276. 

A  mixed  number  is  so  called  when  the  decimal  point  is  placed 
between  two  of  the  figures,  as  shown  in  the  following  number:  27.6 
is  27  decimal  6. 

If  the  figures  were  placed  like  this,  2.76,  then  it  would  be  2  deci- 
mal 76. 

A  number  like  this  is  6  whole  numbers,  6. 

A  number  like  this  is  6  tenths,  .6 

A  number  like  this  is  6  hundredths,  .Ofi 

A  number  like  this  is  6  thousandths,  .006 
and  the  values  decrease  in  the  same  manner,  according  to  the  num- 
ber of  ciphers  placed  between  the  unit  and  the  decimal  point. 

Addition  of  Decimals. 

Example.  986.25 

2.67 

1493.14 

65.04 


Ans.    2547.10 

There  must  be  two  decimal  figures  in  the  answer,  because  there 
are  two  decimals  in  the  numbers  added. 


10  Taylor's  Modern  Navigation-, 


Example.  2.586 

483.2 
56.9152 


Ans.  542.7012 

Here  it  will  be  seen  that  decimals  are  placed  under  decimals  ac- 
cording to  their  value,  and  also  that  the  four  figures  to  the  right, 
in  the  answer,  are  decimals,  because  in  one  of  the  numbers  there 
are  also  four  decimal  figures. 

Subtraction  of  Decimals. 

Example.  From        2698.726 

Subtract     523.973 


Ans.  2174.753 

Subtract  in  the  same  manner  as  common  numbers,  but  count  off 
to  the  right  as  many  figures  as  you  have  decimals  in  the  larger  deci- 
mal number,  and  place  the  dot,  or  decimal  point. 

Example.  From        1090.263 

Subtract       82.3 


Ans.  1007.963 

It  will  be  noticed  in  this  case  that  in  one  number  there  are  three 
decimals  and  in  the  other  only  one;  so  you  must  point  off  three 
figures  to  the  right. 

Example.  From        26.000 

Subtract       .987 

Ans.  25.013 

Here  one  number  is  a  whole  number  and  the  other  entirely  deci- 
mals; so  it  is  necessary  to  place  to  the  right  of  the  26  three  ciphers, 
to  enable  you  to  subtract,  borrowing  one  from  the  whole  number, 
as  seen  in  example. 

Multiplication  of  Decimals. 

Example.  Multiply  26.58  by  4.2. 

4.2 

5316 
10632 


111.63G 


Decimals.  11 


Multiply  in  same  manner  as  common  numbers,  but  point  off 
from  the  result  as  many  figures  as  are  contained  in  the  two  num- 
bers.    In  this  case  there  are  three. 

Example.  Multiply  89.73  by  41.26. 

41.26 


23838 
7946 
3973 
15892 

1639.2598 

Here  we  point  off  four  figures  as  decimals,  because  there  are  four 
decimals  contained  in  the  problem. 

Note. — Always  cross  off  from  the  result  as  many  figures  as  there 
are  decimals  contained  in  the  two  numbers.  Eemember  that  it  is 
very  important  that  the  decimal  point  be  placed  in  its  proper  posi- 
tion. 

DIVISIO^  OF  Decimals. 

When  any  number  is  divided  by  a  lesser  one,  the  result  is  a  whole 
number. 

When  any  number  is  divided  by  a  greater  one,  the  result  is  a 
decimal  number. 

It  is  not  necessary,  in  the  practice  of  navigation,  to  work  deci- 
mals to  more  than  two  places. 

^a:am/)Ze.— Divide  672.08  by  26.9. 

26.9)672.08(24.9 
538 


1340 
1076 

2648 
2421 


227 
Divide  by  same  rule  as  for  common  numbers,  and  from  the  result 
point  off  one  figure,  because  the  number  divided  contains  one  more 
decimal  figure  than  the  divisor. 
Example.— DWidiQ  330  by  825. 

825)330.0(.4 
3300 


12'  Taylor's  Modern  Xavigatiox. 


Here  one  number  is  divided  by  a  greater  one ;  so,  annex  a  cipher 
to  the  right  and  divide.    The  result  in  this  case  is  .4,  or  four  tenths. 

^a-am/;Ze.— Divide  2.5872  by  2.4. 

2.4)2.5872(1.078 
24 

187 
168 

192 
192 

Here  there  will  be  three  decimals,  because  the  number  divided 
has  three  more  decimals  than  the  divisor.  If  there  should  be  a  re- 
mainder, borrow  a  cipher  and  again  divide  until  you  have  as  many 
decimals  as  you  may  think  are  required. 

EuLE  TO  Convert  a  Fraction  Into  a  Decimal. 

Bring  the  top  figure  down,  annex  a  cipher  to  it,  and  divide  by 
the  lower.  The  result  will  be  a  decimal  number  equal  to  the  frac- 
tion. If  necessary,  annex  another  cipher,  or  as  many  as  may  be,  in 
the  student's  opinion,  needed.  In  this  case  the  number  is  .54,  as 
per  example. 


Thus,  27 


50)  270  (.54 
250 

200 
200 


A  Short  Method  to  Reduce  Minutes  of  an  Hour  to  a  Decimal 
OF  AX  Hour. 

There  are  fiO  minutes  in  an  hour,  therefore  10  into  60  will  go  6 
times;  so  6  minutes  is  one  tenth  part  of  an  hour. 

So,  to  convert  minutes  into  decimals,  simply  divide  them  by  6. 
This  will  give  tenths.  If  there  should  be  a  remainder,  annex  n 
cipher  to  it,  and  again  divide.     The  result  will  be  hundredths. 

Example.  6)42 

.7  (tenths). 


DECIMALS.  13 


Example.  6) 51  (.85   (hundredths). 

48 


EuLE  TO  Convert  Hours  and  Minutes  of  Time  Into  Decimals 
OF  A  Day. 

Divide  the  minutes  by  6  and  place  the  result  to  the  right  of  the 
liours,  then  divide  by  24. 

Example.— 2V'  SG'". 

24) 21.6 (.9   (tenths  of  a  day). 
21.6 

Example— 18^  24'". 

24)  18.4 (.76  (hundredths). 
168 

160 
144 


EuLEs  OF  Three,  or  Proportion. 

If  a  ship  sail  7.3  miles  in  one  hour,  how  many  miles  will  she 
sail  in  24  hours? 

7.3 

24 

2CK2 
146 


175.2  (175  miles  and  2  tenths). 

If  a  ship  is  sailing  at  the  rate  of  18  miles  per  hour,  how  much 
v.-ill  she  make  in  20  minutes? 

1  hour. 
60°^    :  20'"    ::  18  miles. 
20 

60)360(6  miles. 
360 


14  Taylor's  Modern  Navigation. 

If  a  chronometer  alter  26"'  40^  in  40  days,  how  much  will  it  alter 
in  one  clay? 

40    :  1    ::  26™  40« 
60 

1600 
1 

40)1600(40^  per  day. 
160 


ADDITION  OF  DEGREES,  MINUTES,  AND  SECONDS. 

60  minutes  make  1  de- 


Sixty 

second  s 

(■' 

') 

make  1 

minute 

(') 

gree  (°) 

Add- 

41° 

21 

15 

'  21' 
41 
14 

41' 
15 
12 

78°  17'  08" 

The  sum  of  the  seconds  being  68",  and  as  there  are  only  60"  in 
1',  we  must  put  down  what  is  over  the  60"  and  carry  the  1'  to  the 
minutes;  the  sum  of  the  minutes  being  77',  and  as  there  are  only 
60'  in  1°,  we  must  put  down  what  is  over  the  60'  and  carry  the  1° 
to  the  degrees. 

Add— 


20° 

57' 

50' 

11 

48 

57 

14 

50 

40 

47°  37'  27" 

The  sum  of  the  seconds  in  this  case  is  147" ;  this  sum  divided  by 
60"  will  give  2'  and  27" ;  carry  the  2'  to  the  minutes,  and  we  get 
the  sum  of  157',  which  is  2°  and  37';  carry  the  2°  to  the  degrees 
and  add,  and  we  get  the  sum  of  degrees. 

Examples  for  Practice. 

(1)    11°   57'  25"  (2)    96°   10'     2"  (3)    17°   59'     1" 

13     16    29  60     15      0  57       1    23 

74     52    18  7       4    59  108     58    59 


SUBTHACTIOX MlLTU'LICATION.  15 


(4)  13°  14'  15"      (5)  41°  40'  50"      (6)  11°  2'  59' 
16  17  18  27  16   0  73  47  11 

19  20  21  2  59  59  18  33  44 


Answers. 

(1)    100°  06'  12"  (2)    163°  30'     1"  (3)    183°  59'  23" 

(4)     48°  51'  54"  (5)      71°   56'  49"  (6)    103°  23'  54' 


SUBTEACTION  OF  DEGREES,  MI^^UTES,  AND  SECONDS. 

Example.  27°  20'  40" 

19     30    50 


7°  49'  50" 

As  I  cannot  take  50"  from  40",  I  must  borrow  1'  and  add  it  to 
the  seconds;  now,  as  1'  is  equal  to  60".  if  I  add  it  to  the  40"  it  will 
make  it  100",  and  I  then  say,  50"  from  100" ;  then,  as  we  have 
taken  1'  from  the  20',  we  must  say  30'  from  19',  and  as  we  cannot, 
let  us  borrow  a  degree  and  add  it  to  the  minutes,  which  will  make 
the  minutes  79';  now  we  can  take  30'  from  79';  then,  as  we  have 
borrowed  1°,  we  must  say  19°  from  26°. 

Examples  for  Practice. 

(1)     45°  29'  17"  (2)    18°  59'  17"  (3)   29°   51'  41" 

27     43    24  17     58    43  17     22    52 


(4)   120°  49'  59"  (5)    91°  23'     1"  (6)   23°  41'  15' 

100     51    00  14     52    57  11     41    59 


Answers. 

(1)    17°  45'  53"  (2)      1°  00'  34"  (3)    12°  28'  49" 

(4)   19°   58'  59"  (5)   76°  30'     4"  (6)    11°   59'  16" 


MULTIPLICATION     OF     DEGREES,     MINUTES     AND 
SECONDS. 

Multiply  47°  50'  40"  by  2 

2 


95°  41'  20' 


16  Taylor's  Modern  Xavigation. 

Twice  40"  is  80" ;  80"  is  therefore  1'  and  20" ;  put  down  the  20" 
and  carry  the  1';  twice  50'  is  100',  and  1  more  is  101';  101'  is  1° 
ard  41';  put  down  the  41'  and  carry  the  1° ;  then  twice  47°  and  1° 
are  95°. 

Multiply  19°  10'  59"  by  3 
2 


38°  21'  58' 


Twice  59"  is  118",  which  is  1'  and  58";  put  down  the  58"  and 
carry  the  1';  twice  10'  is  20'  and  1'  is  21';  put  down  this  21',  be- 
cause it  is  less  than  60';  then  twice  19°  is  38°. 

Examples  for  Practice. 

Multiply  (1)  17°  58'  40";  (2)  59°  16'  52";  (3)  71°  59' 
59";  (4)   89°  59'  14"  by  2. 

Answers.— (1)  35°  57'  20";  (2)  118°  33'  44";  (3)  143°  59' 
58";  (4)    179°   58'  28". 

Multiply  82°  42'  52"  by  4 
4 


330°   51'  28" 


Four  times  52"  are  208",  which  is  equal  to  3'  and  28" ;  carry 
the  3';  then  4  times  42'  and  3'  are  171',  which  is  equal  to  2°  and 
51';  then  4  times  82°  and  2°  are  330°. 

Examples  for  Practice. 

Multiply  (1)  9°  50'  41";  (2)  10°  17'  18";  (3)  19°  24'  30"; 
(4)  98°  42'  15"  by  4. 

Answers.— {1)     39°  22'  44";     (2)     41°   9'  12";     (3)     77°   38' 
00";  (4)  394°  49'  0". 


DIVISIOX  OF  DEGEEES,  MINUTES,  AND  SECONDS. 

Divide  71°   53'  40"  by  2. 

2)71°   53'  40" 
35°  56'  50" 


Indices.  17 


Two  will  go  into  71°  35  times  and  1  over;  carry  this  1°  and  add 
it  to  the  minutes;  it  will  now  be  GO';  then  60'  and  53'  are  113'; 
then  2  into  113',  and  we  get  56'  and  1  over;  carry  this  minute  to 
the  seconds,  and  we  get  100" ;  divide  it  by  2  and  we  get  50". 

Examples  for  Practice. 

(1)   2)27°   IT'  14"        (2)   2)89°   59'  50"         (3)   2)17°  40'  18" 

(4)  2)5°  51'  58"        (5)   2)120°  49'  57"        (6)   2)89°  59'  16" 

Answers.— (1)  13°  38'  37";  (2)  44°  59'  55";  (3)  8°  50'  9"; 
(4)  2°  55'  59";  (5)  60°  24'  58";  (6)  44°  59'  38". 

Divide  97°  50'  12"  by  4. 

4)97°  50'  12" 
24°  27'  33" 

Four  into  97°  will  go  24  times  and  1  over;  then,  1°  being  equal 
to  60',  you  must  add  60'  to  the  50'  and  divide  by  4;  after  dividing 
the  minutes  by  4  you  find  that  you  have  2'  left ;  add  these  2'  to  the 
seconds,  which  will  make  132",  and  divide  again  by  4.  If,  after 
you  have  divided  the  seconds,  you  have  anything  left  over,  let  it  go. 

Note. — In  actual  sea  practice  it  is  unnecessary  to  work  to  sec- 
onds of  arc. 

Examples  for  Practice. 
(1)   4)89°   51'  20"       (2)   4)13°   59'  18"        (3)   4)173°   20'  40" 

(4)  4)101°  38'  42"    (5)  4)50°  43'  50"    (6)  4)179°  1'  0" 

Answers.— (1)  22°  27'  50";  (2)  3°  29'  49":  (3)  43°  20' 
10";  (4)  25°  24'  40";  (5)  12°  40'  57";  (6)  44°  45'  15". 


LOGARITHMIC  INDICES.  ; 

As  multiplication  and  division  by  logarithms  are  sufficiently  ex- 
plained in  Bowditch,  I  will  not  treat  of  them  here,  but  will  give  a 
few  illustrations  of  how  the  index  of  a  number  may  be  found. 

Tayi,or's  Mod.   Nav.   2. 


i8  Taylor's  jModern  Navigation. 


The  index  of  a  whole  numher  is  always  one  less  than  the  number 
of  figures.  For  instance,  if  a  number  consist  of  six  figures,  the 
index  will  be  five;  expressed  thus:  5. 

Examples  to  Illustrate. 


Whole  Numb 

ers. 

9. 

Index 

0. 

22. 

Index 

1. 

501. 

Index 

2. 

7983. 

Index 

3. 

82645. 

Index 

4. 

157867. 

Index 

5. 

2763948. 

Index 

6. 

82171619. 

Index 

7. 

Mixed  Numb 

ers. 

1.9        Index  0,  because  1  figure    in  whole  number. 

22.40      Index  1,  because  2  figures  in  whole  number. 

80.7809  Index  1,  because  2  figures  in  whole  number. 

896.32      Index  2,  because  3  figures  in  whole  number. 

5680.276    Index  3,  because  4  figures  in  whole  number. 

79648.9242  Index  4,  because  5  figures  in  whole  number. 

If  the  number  consist  of  decimals  only,  the  index  is  9.  when 
there  are  no  ciphers  following  the  decimal  point,  and  one  less  for 
every  cipher  that  follows  the  decimal  point;  thus: 


.2 

Index 

is  9. 

.02 

8. 

.002 

1-! 
i  . 

.0002 

6. 

.00002 

789 

5. 

And  so  on. 

TO  CORRECT  COMPASS  COURSE  IN  POINTS. 

Allow  first  the  leeway,  then  the  deviation,  then  the  variation. 

Easterly  variation  and  deviation  always  allow  towards  the  right 
hand,  and  westerly  towards  the  left  hand,  when  finding  the  true 
course  from  the  compass  course.  The  student  must  always  imagine 
himself  standing  in  the  center  of  the  compass,  looking  towards  the 
edge  of  the  card. 


CoKRErnxG  CoiusES.  19 


Example. 

Course.  Wind.  Leeway.  Dev.  Var. 

N.E.  N.N.W.  2  points.  1  point  E.  3  points  W. 

Now,  as  the  wind  is  driving  the  ship's  head  more  to  the  East,  and 
as  she  is  making  two  points  leeway,  it  is  easily  to  be  seen  that  she 
must  be  making  an  E.N.E  course.  Now  stand  in  the  center  of  the 
compass  and  look  at  the  E.N.E.,  then  allow  the  1  point  easterly 
deviation  to  the  right,  and  you  will  be  at  the  E.XN.  point.  Now 
look  at  the  E.XN".  point,  allow  the  3  points  westerly  variation  to 
the  left,  and  you  will  find  it  to  be  N.E..  which  is  the  true  course. 

Example. 

Course.  Wind.  Leeway.  Dev.  Var. 

N.XW.        W.XN.         li  points.         1  point  W.  2  points  E. 

Now,  as  the  wind  is  driving  the  ship's  head  more  N.,  and  the  lee- 
way being  I14  points,  it  will  be  seen  that  the  ship  must  be  making 
a  N.>4E.  course  through  the  water;  face  N.J^E.,  then  allow 
the  1  point  W.  deviation  to  the  left,  and  you  will  have  N.VjW. ;  face 
N.i/oW.  and  allow  the  2  points  E.  variation  to  the  right,  and  you 
will  have  N.XE.i^E.,  which  is  the  true  course. 

Example. 

Course.  Wind.  Leeway.  Dev.  Var. 

W.  N.N.W.  1  point.  U  pts.  W.        2^  pts.  E. 

In  this  case  the  wind  is  driving  the  ship's  head  to  the  South,  and 
she  would  be  making  a  W.XS.  course;  then  allow  the  1%  points 
W.  deviation  to  the  left,  and  we  get  S.W.XW.i/^W.;  facing  this 
point  and  allowing  the  variation  2^  points  E.  to  the  right,  we  have 
W.14S.,  which  is  the  true  course. 

Examples  for  Practice.  '' 


Course. 

Wind. 

Leeway. 

Deviation. 

Variation. 

Answer. 

N.XE. 

E.XN. 

1  pt. 

2  pts.  E. 

\  pt.  W. 

N.XE.^E. 

S.S.E. 

s.w. 

1^  pts. 

U  pts.  W. 

2  pts.  W. 

E.XS.iS. 

E.XS. 

S.XE. 

2  pts. 

3  pts.  E. 

5  pts.  W. 

N.E.XE. 

S. 

E.S.E. 

3  pts. 

2^  pts.  W. 

4  pts.  E. 

s.w.nv. 

w. 

N.N.W. 

ipt. 

\l  pts.  E. 

2  pts.  E. 

N.W.XW. 

E. 

N.N.E. 

Ipt. 

U  pts.  W. 

3  pts.  E. 

S.E.XE.fE 

N. 

E.N.E. 

2  pts. 

\  pt.   W. 

Ipt.    W. 

N.W.I  W. 

20  Taylor's  Modern  Navigation. 

j^ote.—The  X  marked  between  the  letters  indicating  the  courses 
means  the  word  "by";  thus,  N-XW.  means  "north  by  west." 

TO  COERECT  A  COURSE  IN  DEGREES  AND  MINUTES. 

First  apply  the  leeway  to  the  course,  which  is  generally  given  in 
points;  then  turn  the  result  into  degrees  by  noting  how  many 
points  and  quarter-points  the  course  is  from  the  North  or  South, 
referring  to  the  table  of  the  angles  given  in  first  part  of  book; 
then  apply  the  deviation  and  next  the  variation,  easterly  to  the 
right  and  westerly  to  the  left. 

Example. 

Course.  Wind.  Leeway.  Dev.  Var. 

S.W.  S.S.E.  U  points.  10°  E.  17°  W. 

S.  59°  4'  W. 
Dev.  10    0    E. 


S.  69    4  W. 
Var.  17    0  W. 


True  course,  S.  52°  4'  W. 

The  course  being  S.W.  and  the  wind  being  S.S.E.,  it  will  be  seen 
that  the  wind  is  driving  the  ship's  head  more  to  the  West,  and 
therefore  she  must  be  making  a  S.W.XW.I/4W.  course  by  compass, 
which  is  51/4  points  from  South.  By  referring  to  the  table  of  the 
angles  you  will  find  59°  3'  45"  opposite  514  points;  this  will  be 
S.  59°  4'  W.,  nearly.  Now  stand  in  the  center  of  the  card  and 
face  towards  this  course,  and  allow  the  deviation  10°  E.  to  the 
right,  and  you  will  see  that  you  are  going  away  from  South 
(the  point  that  you  are  reckoning  from),  and  therefore  you  must 
add  the  10°  E.  deviation.  Now  apply  the  variation  17°  W.,  and 
allow  it  to  the  left,  and  you  will  be  going  towards  the  South  this 
time;  so  you  must  subtract.     The  result  will  be  the  true  course. 

Example. 

Course.  Wind.  Leeway.  Dev.  Var. 

N.XE.  E.  2  points.  20°  E.  14°  W. 

The  course  after  the  leeway  is  applied  is  N.XW.,  which  is  one 
point  from  North;  this,  turned  into     degrees,  is  N.  11°  15'  W.; 


Correcting  Coursks.  21 

then  allow  the  deviation  20°  E.  to  the  right,  hy  subtracting  the  N. 
11°  15'  W.  from  the  deviation  20°  E.,  and  you  get  N.  8°  45'  E.; 
then  allow  the  14°  W.  variation  to  the  left,  and  you  must  subtract 
the  top  from  the  bottom  again  in  this  case,  and  you  will  have 
N.  5°  15'  W.,  which  is  the  true  course.     Thus: 

Course,  N.  11°  15'  W. 
Dev.  20    00  E. 


N.    8    45  E. 

Var.             14    00   W. 

True  course,  N.    5°  15'  W. 

Example. 

Course. 

Wind.       Leeway.           Dev. 

Var. 

W.XN. 

N.             1  pt.             19°  E. 

Course,  S.    90°  00'  W. 
Dev.             19    00  E. 

S.  109    00  W. 
Var.             25    00  E. 

S.  134    00  W. 
180    00 

25°  E 

True  course,  N.  46°  00'  W. 

In  this  case,  after  allowing  the  leeway,  the  course  will  be  West, 
which  is  8  points  from  the  South,  and  turned  into  degrees  it  is 
S.  90°  0'  West.  Allowing  the  deviation,  19°  E.,  to  the  right,  it 
is  seen  that  we  are  going  away  from  the  South,  which  is  the  point 
we  are  reckoning  from,  and  therefore  we  must  add ;  then  allow  the 
variation,  25°  E.,  and  as  we  are  still  going  away  from  the  South 
we  must  certainly  add.  We  then  have  S.  134°  W. ;  now  square  this 
up  by  subtracting  it  from  180°  and  change  the  name  of  South  to 
North,  and  the  result  is  the  true  course.  After  a  little  practice, 
and  by  studying  the  compass-card,  the  reason  why  you  subtract 
from  180°  will  be  seen. 


22  Taylor's  Modern  Navigation, 


Examples  for  Practice. 

Course. 

Winds. 

Leeway.      Dev. 

Var. 

Answers. 

1. 

N.N.E. 

N.W. 

n  Pt.     10°  E. 

5°  W. 

N.  55°  38'  E. 

2. 

W.N.W 

N. 

H    "         5    E. 

10    E. 

N.  69   23    E. 

3. 

s.w.xw.  s. 

i   "       17    W. 

2    E. 

S.  44     4    W. 

4. 

s.xw. 

W.XS. 

^    "       20    W. 

17    E. 

S.     2    38    W. 

5. 

S.S.E. 

E. 

\\    "       24    E. 

21    E. 

S.  39   22    W. 

6. 

E.iS. 

s. 

i   "       11    W. 

7    W. 

N.  74   49    E. 

7. 

E.XN. 

S.S.E. 

\   "       27    E. 

2    W. 

S.  81    52    E. 

The  true 

course  will 

never  be  more  1 

than  90°; 

so  if  you  have 

more  after  i 

illowing  the 

I     corrections,  subtract  it  from     180°  and 

change  the  name  of  North  to  South,  or  South  to  North,  as  the  case 
may  be.  If  you  have  just  90°,  it  will  be  due  East  or  due  West. 
Thus,  suppose  you  had  S.  90°  0'  W.,  you  would  call  it  West;  and 
suppose  you  had  N".  90°  0'  E.,  you  would  call  it  East;  and  so  on. 
North  is  no  degrees  and  South  is  no  degrees;  they  are  just  plain 
North  or  South. 

THE  DAY'S  WORK,  OE  THE  RULE  TO  FIND  THE  POSI- 
TION OF  SHIP  BY  DEAD-RECKONING. 

The  elements  required  to  work  this  problem  are  the  courses 
steered  and  the  distances  sailed  on  each.  We  must  also  know  the 
deviation  for  each  point,  which  must  have  been  determined  at  some 
time  before  the  working  of  the  problem  and  noted  in  a  compass- 
book  kept  for  the  purpose. 

Variation. — The  variation  of  the  compass  will  always  be  found 
(,n  th'j  chart  of  the  locality  that  you  happen  to  be  in  at  the  time. 

The  Departure. — When  leaving  a  port  it  is  always  the  custom  to 
take  a  departure  from  a  certain  point,  the  latitude  and  longitude  of 
it  being  taken  from  the  chart,  or  from  the  table  of  Maritime  Posi- 
tions in  the  Bowditch  Epitome.  The  bearing  of  the  point  by  the 
compass  and  the  distance  oft'  is  then  noted,  also  the  deviation  for 
the  direction  of  the  ship's  head  at  the  time.  Now,  as  we  have  to 
reckon  as  if  we  had  actually  sailed  from  the  point,  it  will  be  easily 
seen  that  we  must  turn  the  bearing  right  around;  then  apply  the- 
deviation  for  the  direction  of  the  ship's  head  at  the  time  the  bear- 
ing was  taken,  and  then  the  variation  to  get  the  true  course,  or  de- 
parture course,  as  it  is  sometimes  called. 


])A\'S     WOKK.  23 


Example. — The  bearing  of  a  point  of  land  being  N.W.XW.I/4W., 
the  opposite  to  it  must  be  S.E.XE.l^E.,  this  being  5i/4  points  from 
South.  Turned  into  degrees,  it  is  S.  59°  4'  E.  The  deviation  and 
variation  is  then  applied,  easterly  to  the  right  and  westerly  to  the 
left.  We  then  have  the  true  course,  which  is  called  the  departure 
course. 

Correcting  Course. — Then  correct  each  course  sailed,  for  the  lee- 
way, deviation,  and  variation,  as  explained  elsewhere. 

Current  Course. — The  current  course,  or  the  set  and  strength  of 
a  current,  is  taken  from  the  chart  or  a  book  of  sailing  directions 
for  that  locality,  and  is  given  magnetic;  therefore  the  only  correc- 
iion  to  be  applied  is  the  variation,  to  get  the  true  set. 

Rate  of  Current. — If  the  rate  of  the  current  is  given  at  the  rate 
per  hour,  all  that  you  have  to  do  is  to  multiply  it  by  the  number  of 
hours  in  a  day,  and  you  will  get  the  amount  it  will  set  in  one  day. 
11  the  set  is  given  at  so  much  per  day,  you  have  only  to  put  the  dis- 
tance given  in  the  traverse  table ;  and  if  you  want  to  know  what  is 
the  rate  per  hour,  divide  by  24. 

Leeway. — The  leeway  is  found  by  observing  the  ship's  wake  and 
noting  the  angle  between  it  and  the  fore-and-aft  line  of  the  ship. 

^Yhen  studying  these  rules,  follow  the  worked-out  examples. 
Figure  by  figure. 

The  departure  bearing  being  E.XS.  in  this  example,  and  the 
opposite  point  being  W.XN.,  which  is  7  points  from  North,  and 
this,  turned  into  degrees,  being  N".  78°  45'  W.,  the  deviation  for 
the  direction  of  the  ship's  head  is  then  applied,  and  afterwards 
the  variation,  when  we  get  the  true  departure  course.  (See  Ex- 
ample.) 

Each  course  is  then  corrected  for  the  leeway,  then  turned  into 
degrees,  and  afterwards  the  deviation  and  variation  is  applied. 

Lastly,  the  current  course  is  corrected  for  the  variation  only, 
as  it  is  magnetic.  All  the  courses  being  corrected,  we  now  proceed 
to  draw  a  traverse  table,  marking  a  column  for  the  corrected 
courses,  one  for  the  distances  sailed  on  each  course, — one  each  for 
N.,  S.,  E.,  and  W.     The  N".  and  S.  columns  are  called  the  Differ- 


24  Taylor's  Modern  Xavigation. 

ence  of  Latitude  columns,  the  E.  and  W.  the  Departure  columns. 
We  now  place  each  of  the  corrected  courses  to  the  nearest  degree 
in  its  proper  column,  commencing  with  the  Departure  course  and 
ending  with  the  Current  course,  marking  the  distances  sailed  on 
each  course  alongside  of  the  true  courses,  the  distance  oflE  the 
point  opposite  the  Departure  course,  and  the  amount  of  current 
opposite  the  Current  course. 

Eefer  to  Table  2  of  Bowditch  and  look  for  the  degree  of  the  first 
course,  and  you  will  find  it  at  the  foot  of  the  page ;  run  your  finger 
up  the  Distance  column  and  find  the  distance;  alongside  of  it  will 
be  found,  in  the  Latitude  column,  1.0,  and  in  the  Departure  column, 
6.9;  put  the  1.0  in  the  IST.  column  because  the  course  is  N.,  and  the 
departure  6.9  in  the  W.  column  because  it  is  W. ;  then  take  each 
course  and  distance  in  its  proper  order  and  do  the  same.  Now 
take  the  last  course  and  look  for  it  at  the  head  of  the  page;  run 
your  finger  down  the  Distance  column  and  find  the  distance ;  along- 
side of  it  will  be  found  18.5  in  the  Latitude  column  and  9.9  in  the 
Departure  column;  put  the  18.5  in  the  S.  column  because  the 
course  is  S.,  and  9.9  in  the  W.  column  because  the  course  is  W. 

We  will  now  suppose  we  have  taken  out  the  difference  of  latitude 
and  departure  for  all  the  courses  and  distances.  Next,  add  the 
N.,  S.,  E.,  and  W.  columns  separately;  subtract  the  IST.  from  the 
S.  or  the  S.  from  the  N".  column,  and  the  E.  from  the  W,  or  the 
W.  from  the  E.,  as  the  case  may  be.  The  difference  between  the 
IS',  and  S.  columns  will  be  the  difference  of  latitude,  and  the  differ- 
ence between  the  E.  and  W.  columns  will  be  the  departure. 

To  Fifiid  the  Latitude  In. — Under  the  latitude  left  put  the  differ- 
ence of  latitude,  and  if  they  are  the  same  name,  add,  but  if 
different  names,  subtract.  The  result  will  be  the  latitude  in.  In 
the  example  the  difference  of  latitude  is  58.9,  or  59'  nearly,  because 
9  lOths  is  nearly  another  mile,  and  it  is  named  N.  because  the  N. 
column  is  the  greater.  Now,  as  the  latitude  left  is  N.  and  the 
difference  of  latitude  is  N.,  we  must  add,  because  we  are  going  away 
fiom  the  equator,  and  must  therefore  increase  our  latitude.  The 
Latitude  in  is  then  38°  59'  N. 

To  Find  the  Middle  Latitude.— \M  the  latitude  in  to  the  lati- 
tude left  and  divide  the  sum  by  2.  The  result  will  be  the  middle 
latitude. 


Day's    Wouk.  25 


To  Find  the  Difference  of  Longitude.— Eniev  Table  2  with  the 
nearest  degree  of  the  middle  Latitude  as  a  course,  and  look  in  the 
Latitude  column  for  the  departure.  When  found,  note  the  distance 
in  the  Distance  column  abreast  of  it.  This  distance  will  be  the 
difference  of  longitude  in  minutes.  If  over  60',  turn  them  into 
degrees  and  minutes  by  dividing  by  60. 

In  the  example  the  middle  latitude  is  38°,  so  we  must  turn  up 
38°  in  Table  2  and  look  for  the  departure  100.5  in  the  Latitude 
column.  It  is  then  found  abreast  of  128  in  the  Distance  column ; 
this  128  is  therefore  the  difference  of  longitude  in  minutes,  which 
divided  by  60  gives  2°  8',  to  be  named  W.  because  the  West  column 
is  the  greater. 

To  Find  the  Longitude  /n.— Under  the  longitude  left  put  the 
difference  of  longitude,  and  if  they  are  the  same  name,  add  ;  if 
different  names,  subtract.  The  result  will  be  the  Longitude  in. 
to  be  named  the  same  as  the  greater  always.  In  the  example  the 
longitude  left  is  123°  W.,  and  as  the  difference  of  longitude  is  also 
W.,  it  must  be  added  to  obtain  the  Longitude  in. 

]\rote.—U  after  applying  the  difference  of  longitude  the  result 
i>  greater  than  180°,  subtract  it  from  360°,  and  change  its  name. 

To  Find  the  Course  and  Distance  made  Good  in  a  Straight  Line. 
—Before  starting  to  find  the  course  and  distance,  see  which  is  the 
greater,  the  difference  of  latitude  or  the  departure, — as  you  must 
rpad  difference  of  latitude  and  departure  at  the  head  of  the  page 
if  the  latitude  is  the  greater,  and  at  the  bottom  if  the  departure  is 
the  greater. 

Look  in  Table  2  until  you  find  the  difference  of  latitude  and 
departure  alongside  of  each  other  in  their  own  columns,  and  when 
you  have  located  them,  the  course  will  be  found  at  the  head  of  the 
page  when  the  difference  of  latitude  is  the  greater  and  at  the  foot 
of  the  page  if  the  departure  is  the  greater.  The  distance  will  be 
found  in  the  distance  column  abreast  of  the  difference  of  latitude 
and  departure.  In  the  example  the  difference  of  latitude  and 
departure  are  found  alongside  of  each  other  on  the  60°  page, 
because  the  departure  is  the  greater,  and  the  distance  abreast  is 
116  miles. 

To  Name  the  Course.— li  the  difference  of  latitude  is  N.,  name  it 
N.;  if  S.,  name  it  S.;  and  towards  the  E.  or  W.  according  as  you 
have  made  difference  of  longitude  to  the  E.  or  W.  In  the  example 
the  course  is  N.  60°  W.  because  the  difference  of  latitude  is  N.  and 
the  departure  is  W. 


26 


Taylor's  Modern  Navigation. 


DAY'S  WORK. 


Hours. 

Courses. 

Knots 

lOths 

Winds. 

Lee- 
way. 

Deviation. 

Remarks. 

Pts. 

1 

N.W.XW. 

5 

N.XE. 

1| 

20°  W. 

A    point,    Pt. 

2 

5 

Reyes,    in    lat. 

3 

5 

38°    N.,   long. 

4 

5 

123°  \V.,  bore  by 

5 

N.N.W. 

4 

5 

N.E. 

2i 

10°  w. 

compass   E.    X 

6 

4 

5 

S.,  distance    7 

7 

4 

miles. 

8 

4 

9 

West 

4 

5 

N.N.W. 

1 

0 

Ship's   head 

10 

3 

5 

N.W.XW. 

11 

3 

5 

12 

3 

5 

Dev.    as    per 

1 

W.N.W. 

7 

North. 

i 

15°  W. 

log. 

2 
3 
4 

i 

Var.   16°    30' 

1 

7 

5 
5 

E. 

5 

N.W. 

7 

5 

W.S.W. 

i 

18°  W. 

A  current  set 

6 

7 

5 

correct       mag- 

7 

7 

5 

netic     s.xw.. 

8 

7 

5 

distance          21 

9 

North 

7 

5 

S.W. 

0 

2°  E. 

miles,  from  the 

10 

6 

5 

time    dep.    was 

11 

6 

5 

taken  to  the  end 

12 

6 

5 

of  day. 

study  the  above  example,  and  at  the  same  time  study  the  rules. 


Day^s  Work.  27 


Examples. 

Dep.  CO.      E.  XS. 
Opposite     W.XN. 

N.  78°  45'  \V. 
Dev.       20    00  W. 


N.  98    45  W 
Var.        16    30  E. 


T.  dep.  CO.  N.  82°  15'  W. 

1st  CO.  N.  75°  56'  W.  4th  co.  N.  70°  19'  W. 

Dev.          20    00   W.  Dev.          15    00  W. 

N.  9^56'  W.  N.  85°  19'  W. 

Var.          16    30  E.  Var.          16    30   E. 

T.  CO.    N.79^'W.  T.  CO.    N.  68°  49' W. 

2d  CO.  N.  47°  49'  W.  5th  co.  N.  39°  23'  W. 

Dev.          10    00  W.  Dev.          18    00  W. 

N.  57°  49'  W.  N.57°23'W. 

Var.          16    30  E.  Var.          16    30  E. 

T.  CO.    N.4T°l9'W.  T.  CO.    N.40°53'W. 

3d  CO.  B.  78°  45'  W.  6th  co.  N.    0°  00' 

Var.           16    30   E.  Dev.             2    00   E. 

S.95^'W.  N.    2°00'E. 

180    00  Var.          16    30  E. 

T.co.    N.il^'W.  T.co.    N.18°30'E. 

Current  CO.      S.  11°  15' W. 

Var.  16    30   E. 


T.  current  co.  S.  27°  45'  W. 


28 


Taylor's  Modern  Navigation. 


TRAVERSE  TABLE. 


Corrected 
Courses. 

Distance. 

Difference  of  Latitude. 

Departure. 

N. 

s. 

E.                               W. 

N.  82°  W. 

7 

1.0 

6.9 

N.  79    W. 

20 

3.8 

19.6 

N.  41    W. 

17 

12.8 

11.2 

N.  85    W. 

15 

1.3 

14.9 

N.  69    W. 

29 

10.4 

27.1 

N.  41    W. 

30 

22.6 

19.7 

N.  19    E. 

27 

25.5 

8.8 

S.  28    W. 

21 

18.5 

9.9 

'7.4 
L8.5 

58.9 

N. 

18.5              8.8               109.3 
8.8 

Diff.  of  lat. 

Lat.  left,    38°00'N. 
59  N. 

Dep.  100.5 

Long,  left,     123°  00'  W. 
Diff.  of  long.     2      8  W. 

Lat.  in       38°  59'  N. 

38    00  N. 

Long,  in,        125°    8'  W. 

2)76°  59' 
Mid.  lat.    38°  29' 

With  difference  of  latitude  58.9  and  departure  100.5,  the  course 
is  N.  60°  W.,  and  distance  IIG  miles. 


Day's   Wokk. 


29 


DAY'S  WORK. 


Hrs. 

Courses. 

Knots. 

lOths 

Winds. 

Ia-c- 

Peviiition. 

Remarks. 

1 

N.N.E. 

14 

7 

East 

Pts. 

2i 

47°  E. 

A  point  in 

2 

12 

3 

lat.   59°    57' 

3 

10 

S.,  long.  0°  5' 

4 

10 

W.,  bore   by 

5 

s.xw. 

8 

E.XS. 

11 

21°  W. 

compass     N. 

6 

7 

W.XW.^W., 

7 

4 

distance     21 

8 

3 

miles. 

9 

W.^N. 

4 

5 

N.N.W. 

^ 

29°  E. 

Ship'shead 

10 

4 

5 

N.N.E. 

11 

4 

5 

12 

4 

5 

Dev.  as  per 

1 

E.S.E. 

4 

N.E. 

2f 

47°  W. 

log. 

2 

4 

Var.      18° 

3 

4 

5 

47'  W. 

4 
5 
6 

7 
8 
9 

10 
11 
12 

N.W.XW.^W. 

4 

5 

6 

6 

7 

9 

13 

14 

15 

5 

S.W. 

1 

22°  E. 

A  current 
set       correct 

magnetic  W. 

X  S.  i  S.  29 

E.iS. 

S.XE. 

i 

19°  W. 

miles  from 
the  time  dep. 

was  vaken  to 
end    of    day. 

30 


Taylor's  Modern  Xavigation. 


TRAVERSE  TABLE. 

Dep.  CO. 
Opposit 

N.W.XW.^W. 

e  S.E.XE.|E. 

S.  61°  53'  E. 

47    00  E. 

Corrected 
Courses. 

Dist. 

Diff.  of  Lat. 

Departure. 

N. 

s. 

E. 

w. 

Dev. 

S.  34°  E. 
N.  23   E. 

S.     9   E. 
N.  80   W. 
N.  78   E. 
N.  47   E. 
N.  52    E. 
S.  57   W. 

21 
47 
22 
18 
17 
24 
51 
29 

43.3 

3.1 

3.5 

16.4 

31.4 

17.4 

21.7 

15.8 

11.7 

18.4 
3.4 

16.6 

40.2 

Var. 

S.  14°  53'  E. 
18   47  W. 

T.  CO. 

1st  CO. 
Dev. 

S.  33°  40'  E. 

N.    5°38'W. 
47    00  E. 

N.41°22'E. 
18    47  W. 

17.7 
17.6 
24.3 

Var. 

97  7     54  9     90  3     59  6 

T.  CO. 

2d  CO. 
Dev. 

N.  22°  35'  E. 

S.  30°  56'  W. 
21    00  W. 

54.9               59.6 
Diff.  of  lat.            42.8  N.  Dep.  30.7  E. 

Var. 

S.    9°56'W. 
18    47  W. 

S.    8°  51'  E. 

N.  90°  00'  W. 
29    00  E. 

Lat.  left,  59°  57' ^       "^          ■■  -    -^    -.-Tr 
43 

».      -Long,  ieit,  u^    D   w  . 
N.                        1      1  E. 

S.      Long,  in,    0°  56' E. 

L 

5' 

T.  CO. 

3d  CO. 
Dev. 

Lat.  in,    59°  14 

2)119   1] 

Mid.  lat.    59°  3. 

Var. 

N.61°00'  W. 
18    47  W. 

With  difference  of  latitude  42.8  and 
departure  30.7,  the  course  is  N.  36°  E. 
and  distance  52  miles. 

T.  CO. 

N.  79°  47'  W. 

S.  36°  34'  E. 
47    00  W. 

4th  CO. 
Dev. 

6th  CO.    S. 
Dev. 

S. 
Var. 

S. 
T.  CO.      N. 

Current  CO. i^ 
Var. 

T.  CO.          f 

90°  00'  E 
19    00  W 

Var. 

S.  83°  34'  E. 
18    47   W. 

109°  00'  E 
18    47   \\ 

S.  102°  21'  PI 
180    00 

127°  47'  E 
180    00 

T.  CO. 

5th  CO. 
Dev. 

N.    77°  39'  E. 

N.    50°  38'  W. 
22    00  E. 

52°  13'  E 

v75°  56'  W 
18    47  ^\ 

Var. 

N.    28°  38'  W. 
18    47   W. 

T.  CO. 

N.    47°  25'  W. 

^.57°  09'  W 

Day's   Work. 


31 


DAY'S  WORK. 


Hrs. 

Courses. 

Knots. 

lOths 

Winds. 

Lee- 
way. 

Deviation. 

Remarks,  Etc. 

Pts. 

1 

s.w. 

2 

3 

8.S.E. 

2^ 

20°  W. 

A  point  in  lat. 

2 

2 

3 

48°  23'  N.,  long. 

3 

2 

B 

124°  44' W.,  bore 

4 

2 

8 

by  compass  East, 

5 
6 

7 

s.s.w. 

4 

West 

1 

10°  W. 

distance  11  miles. 

10 

Ship's  head  S. 

8 

10 

W. 

9 

S.XE. 

10 

S.W.XW. 

2 

2°  E. 

10 

8 

Dev.as  per  log. 

11 

7 

12 

4 

Var.  23°  20'  E. 

1 

S.E. 

2 

5 

s.s.w\ 

^ 

17°  E. 

2 

1 

5 

A   current    set 

3 

0 

5 

correct  magnetic 

4 

0 

5 

N.N.W.  27  miles 

5 

W^est. 

2 

8.S.W. 

i 

27°  W. 

from  the  time  the 

6 

5 

dep.  was  taken  to 

7 

6 

the    end    of    the 

8 

6 

day. 

9 

W.XS. 

7 

8.xw^ 

1 

24°  W. 

10 

7 

11 

8 

12 

8 

Correct  the  departure  course  for  deviation  and  variation;  com- 
pass courses  steered  for  leeway,  deviation,  and  variation;  current 
course  for  variation. 

Find  the  latitude  and  longitude  in,  and  the  course  and  dis- 
tance made  good  by  inspection. 

Answers. 

Dep.  CO.  K  87°  W.  11;  S.  7G°  W.  10;  S.  25°  W.  30;  S.  8°  E.  29; 
S.  10°  E.  5;  N.  88°  W.  19;  S.  87°  W.  30;  N.  1°  E.  27. 

D.  lat.  36.5  S.  Dep.  77.0  W.  Lat.  in,  47°  46'  N.  D.  long.  115' 
W.  T.  CO.  S.  65°  W.  Dist.  86  miles.  Long,  in,  126°  39'  W. 


32 


Taylor's  Modern  Navigation. 


DAY'S  WORK. 


Hrs. 

Courses. 

Knots. 

lOths 

Winds. 

Lee- 
way. 

Deviation. 

Remarks,  Etc. 

Pts. 

1 

East. 

14 

West. 

0 

2°  W. 

Position  noon  yes- 

2 

12 

terday  lat.  51°  50' S., 

3 

11 

5 

long.  178°  10'  E. 

4 

10 

5 

5 

North. 

7 

6 

E.N.E. 

\ 

20°  W. 

Dev.  as  per  log. 

6 

7 

4 

7 

7 

4 

Var.  0°  0'. 

8 

f7 

6 

9 

E.N.E. 

10 

8 

North. 

H 

8°  W. 

A  current  set  cor- 

10 

11 

2 

rect  magnetic  N.N. 

11 

11 

W.  10  miles  during 

12 

12 

3 

the  day. 

1 

S.E. 

8 

2 

s.s.w. 

2 

12°  E. 

2 

7 

2 

3 

6 

4 

4 

6 

, 

5 

S.S.E. 

5 

East. 

1| 

15^°  E. 

6 

5 

7 

5 

8 

5 

9 

West. 

3 

N.N.W. 

8 

0 

10 

2 

11 

2 

12 

1 

Find  the  latitude  and  longitude  in,  and  the  course  and  distance 
made  good  by  inspection. 

Answers. 

1st  CO.  N.  88°  E.  48,  N.  26°  W.  30;  N.  74°  E.  46;  S.  56°  E. 
26;  S.  13°  W.  20;  South  8;  N.  23°  W.  10. 

D.  lat.  8.6.  Dep.  93.2.  Lat.  in,  51°  41'  S.  Long,  in,  179°  20'  W. 
D.  long.  2°  30'  E.  T.  co.  N.  85°  E.  Dist.  93  miles. 


Day's   Work. 


33 


DAY'S  WORK. 


10 
11 
12 


S.S.W 


South. 


West. 


N.XE, 


East. 


E.XS. 


(> 

r) 

6 

5 

(i 

5 

5 

5 

5 

5 

5 

ry 

5 

5 

5 

4 

4 

4 

1 

1 

1 

1 

2 

5 

5 

2 

8 

Lee 
way. 


S.E. 


E.S.E. 


S.S.W 


N.W. 


N.N.E. 


N.E. 


Pts. 

4|   18^°  W 


10°  W 


H 


51 


A  point,  Yaquina 
Head,  in  lat.  44° 
40'  N.,  long.  124°  5' 
W.,  bore bv  compass 
N.xE.,  distance  17 
miles. 


30°  W 


12°  E. 


40°  E. 


10°  E. 


Remarks,  Etc. 


w 


Ship's   head  S.S. 

Dev.  as  per  log. 
Var.  20°  40'  E. 


A  current  set  the 
ship  N.xE.  correct 
magnetic  3  miles 
from  the  time  the 
departure  was  taken 
to  the  end  of  the 
day. 


Find  the  latitude  and  longitude  in,  and  the  course  and  distance 
made  good  by  inspection. 

Answers. 

Dep.  CO.  S.  13^  W.  IT;  S.  78°  W.  27;  S.  44°  W.  22;  N.  88"  W. 
i:;  X.  52°  E.  4,  S.  12°  E.  13;  S.  17°  W.  30;  N.  32°  E.  3. 

D.  lat.  83.(3  S.  Dep.  61. 7  W.  Lat.  in,  43°  16'  N.  D.  long.  86. 
Long,  in,  125°  31'  W.    T.  co.  S.  36°  W.    Dist.  104  miles. 


Taylor's   Mod.   Nav.   3. 


3-i 


Taylor's  Modern  Navigation. 


DAY'S  WORK. 


Hrs. 

Courses. 

Knots. 

lOths 

Winds. 

Lee- 
way. 

Deviation. 

Remarks,  Etc. 

Pts. 

1 

West. 

11 

E.XS. 

0 

2°  E. 

A  point  in  lat. 

2 

11 

37°  42'  N.,  long. 

3 

10 

123°  00'  W.,bore 

4 

8 

by  compass  E.X 

5 

W.S.W. 

7 

5 

N.W. 

li 

10°  E. 

S.^S,  distance  20 

6 

7 

5 

miles. 

7 

7 

5 

8 

7 

5 

Ship's        head 

9 

South. 

7 

W.S.W. 

If 

27°  E. 

West. 

10 

7 

11 

7 

Dev.  as  per  log. 

12 

7 

1 

N.W. 

5 

W.S.W. 

i 

11°  W. 

Var.  16°  10'  E. 

2 

4 

3 

4 

A  current    set 

4 

4 

correct  magnetic 

5 

N.XE. 

4 

5 

N.W.XW. 

2 

30°  W. 

W.S.W.  22  miles 

6 

5 

5 

from  the  time  the 

7 

6 

5 

departure       was 

8 

4 

5 

taken  to  the  end 

9 

East. 

0 

5 

S.S.E. 

6 

2°  W. 

of  the  day. 

10 

0 

5 

11 

0 

5 

12 

0 

5 

Find  the  latitude  and  longitude  in,  and  the  course  and  distance 
made  good  by  inspection. 

Answers. 

Dep.  CO.  N.  55°  W.  20;  N.  72°  W.  40;  S.  80°  W.  30;  S.  23°  W. 
28;  N.  34°  W.  17;  N.  20°  E.  21;  N.  37°  E.  2.  Current  co.  S. 
84°  W.  22'. 

D.  lat.  26.0  N.  Dep.  117.8  W.  Lat.  in,  38°  8'  N.  D.  long. 
149.    Long,  in,  125°  29'  W.    T.  co.  N.  771/2°  W.    Dist.  120  miles. 


Day's   Work. 


35 


DAY'S  WORK. 


Hrs. 

Courses. 

Knots. 

lOths 

Winds. 

Lee- 
way. 

Deviation. 

Remarks,  Etc. 

Pt,s. 

1 

E.^N. 

2 

5 

N.XE. 

i 

27°  E. 

A  point  in 

2 

2 

5 

lat.O°0',long. 

3 

4 

0°  0',  bore  })y 

4 

5 

compassEast, 

5 

W.iS. 

7 

6 

S.  X  W. 

1 

29°  W. 

distance      14 

6 

8 

8 

miles. 

7 

8 

8 

8 

8 

8 

Ship's  head 

9 

8 

7 

E.^N. 

10 

8 

3 

11 

N.|E. 

7 

5 

E.XN. 

^ 

12°  E. 

Dev.  as  per 

12 

6 

5 

log. 

1 

6 

5 

2 

6 

5 

Var.  1°  52' 

3 

E.XS.fS. 

6 

South. 

1| 

19°  E. 

E. 

4 

4 

5 

4 

A     current 

6 

4 

set  South  cor- 

7 

N.W.XW4W. 

6 

3 

N.^E. 

2i 

31°  W. 

rect  magnetic 

8 

6 

n 
1 

12  miles  from 

9 

6 

8 

time  dep.  was 

10 

6 

8 

taken   to  end 

11 

6 

8 

of  day. 

12 

6 

6 

Find  the  latitude  and  longitude  in,  and  the  course  and  distance 
made  good  by  inspection. 

Answers. 

Dep.  CO.  N.  61°  W.  14;  S.  64°  E.  14;  S.  68°  W.  51;  N.  17°  E. 
27;  S.  69°  E.  18;  S.  &Q°  W.  40.     Current  co.  S.  2°  W.  12. 

D.  lat.  27.4  S.  Dep.  59.1  W.  Lat.  in,  0°  27'  S.  Long,  in,  0° 
59'  W.    T.  CO.  S.  65°  W.    Dist.  65  miles. 

It  will  be  noticed  in  this  example  that  the  latitude  is  practically 
zero;  so  whenever  the  latitude  or  middle  latitude  is  less  than  1°, 
the  departure  will  be  the  difference  of  longitude. 


36 


Taylor's  Modern  Navigation. 


DAY'S  WORK. 


S.E4S. 


N.E.XE. 


E.^N. 


E.4S. 


S.XE.^E. 


Winds.     1^^^;    Deviation 


E.N.E. 


N.XW, 


N.XE. 


N.N.E. 


E.XN. 


u 


H 


10°  w 


18°  E. 


Remarks,  Etc. 


E. 


29°  E. 


5°  W. 


Sandy  Hook 
light-ship,  in  lat. 
40°  29'  N.,  long. 
73°  49'  W.,  bore 
by  compass  N., 
distance  2  miles. 

Ship's  head  S. 
E.|S. 

Dev.  as  per  log. 

Var.  9°  20'  W. 

A  current  set 
correct  magnetic 
N.  E.  X  E.  11 
miles  from  the 
time  the  dep.  was 
taken  to  the  end 
of  the  day. 


Find  the  latitude  and  longitude  in,  and  the  course  and  distance 
made  good  by  inspection. 

Answers. 

Dep.  CO.  S.  19°  E.  2;  S.  53°  E.  38;  N.  T3°  E.  38;  S.  64°  E.  20; 
S.  42°  E.  50;  S.  5°  W.  15.    Current  co.  X.  47°  E.  11. 

D.  lat.  67.1  S.  Dep.  125.5  E.  Lat.  in,  39°  22'  S.  D.  long.  164'. 
T.  CO,  S.  62°  E.    Dist.  142  miles. 


Day's   Work. 


37 


DAY'S  WORK. 


Hrs. 

Courses. 

Knots. 

lUths 

Winds. 

Lee- 
Way. 

Deviation. 

Remarks,  Etc. 

rts. 

1 

N.W. 

4 

5 

N.N.E. 

1| 

2°E. 

Cape  Men- 

2 

4 

5 

docino,     in 

3 

4 

5 

lat.   40°  26' 

4 

4 

5 

N.,        long. 

5 

WA  N. 

3 

5 

N.N.W. 

i 

14°  E. 

124°  24'  W., 

B 

3 

5 

borebycom- 

7 

3 

5 

pass  E.S.E., 

8 

3 

5 

distance     6 

9 

W.S.W. 

4 

5 

N.W. 

2i 

17^°  E. 

miles. 

10 

6 

5 

Ship's 

11 

6 

5 

head    N.W^ 

12 

5 

5 

Dev.      as 

1 
2 
3 
4 

S.W.XW.iW. 

5 
4 
3 
3 

5 
3 

5 

N.^v.^w. 

U 

18°  E. 

per  log. 

Var!    18° 
O'E. 

5 

N.XW. 

3 

W.XN. 

1 

11°  W. 

A  current 

6 

3 

set     correct 

7 

9 

magnetic  N. 

8 

3 

W.    i    mile 

9 

N.W.XN.IN. 

5 

2 

South. 

0 

7°  W. 

from      time 

10 

6 

5 

dep.  was  ta- 

11 

7 

3 

ken   to  end 

12 

8 

of  day. 

Find  the  latitude  and  longitude  in,  and  the  course  and  distance 
made  good  by  inspection. 

Answers. 

Dep.  CO.  N.  48°  W.  6;  N.  45°  W.  18;  N.  58°  W.  14;  S.  78°  W. 
23;  S.  84°  W.  17;  N.  7°  E.  11;  N.  14°  W.  27.  Current  co.  N.  27° 
W.  12. 

D.  lat.  65.3  N.  Dep.  79.1  W.  Lat.  in,  41°  31'  N.  D.  long.  105 
W.    Long,  in,  126°  09'  W.    T.  co.  N.  50°  W.    Dist.  103  miles. 


38 


Taylor's  Modern  Navigation. 


DAY'S  WORK. 


Hrs. 

Courses. 

Knots. 

lOths 

Winds. 

Lee- 
way. 

Deviation. 

Remarks,  Ktc 

Pts. 

1 

s.xw. 

5 

5 

w.x.s. 

i 

15°  E. 

Nantucket  New 

2 

5 

5 

SouthShoallight, 

3 

5 

in  lat.  40°  46'  N., 

4 

5 

long.  69°  56'  W., 

5 

s.w.xw. 

4 

5 

North. 

0 

27°  E. 

bore  by  compass 

6 

4 

5 

N.W.,  distance  7 

7 

4 

5 

miles. 

8 

4 

5 

9 

S.E.iE. 

8 

6 

E.N.E. 

2 

3°E. 

Ship's  head  S. 

10 

12 

8 

xw. 

11 

12 

8 

12 

12 

8 

Dev.     as     per 

1 

East. 

7 

N.N.E. 

^ 

17°  W. 

log. 

2 

6 

3 

6 

Var.  13°  0'  W. 

4 

8 

5 

S.XE. 

14 

5 

E.XS. 

1 

29°  W. 

A   current    set 

6 

14 

5 

correct  magnetic 

7 

14 

W.XS.  10  miles 

8 

14 

from  the  time  the 

9 

North. 

3 

W.N.W. 

31 

19°  E. 

departure  was  ta- 

10 

2 

ken  to  the  end  of 

11 

1 

the  day. 

12 

1 

Find  the  latitude  and  longitude  in,  and  the  course  and  distance 
made  good  by  inspection. 

I  ^  ;  -  ; '.  •■•"M  1  •  Answers. 

Dep.  CO.  S.  43°  E.  7;  S.  10°  W.  21;  S.  70°  W.  18;  S.  35°  E. 
47;  N.  66°  E.  27;  S.  42°  E.  57;  N.  48°  E.  7.  Current  co.  S.  66° 
W.  10. 

D.  lat.  101.3  S.  Dep.  70.2  E.  D.  long.  1°  32'  E.  Lat.  in,  39° 
05'  N.    Long,  in,  68°  24'  W.    T.  co.  S.  35°  E.    Dist.  123  miles. 


Day's   Woi?k. 


39 


DAY'S  WORK. 


Hrs. 

Courses. 

Knots. 

lOths 

Winds. 

Lee- 
way. 

Deviation. 

Remarks,  Etc. 

1 

S.46°E. 

12 

Northerly. 

2° 

5°  E. 

Lat.  left,  47° 

2 

12 

57' N.;  long,  left, 

3 

12 

177°  14'  E. 

4 

12 

5 

12 

Var.    28°    20' 

6 

12 

E. 

/ 

12 

8 

12 

9 

12 

5 

10 

12 

5 

11 

12 

5 

12 

12 

5 

1 

12 

5 

2 

12 

5 

3 

12 

5 

4 

12 

5 

5 

12 

5 

6 

12 

5 

7 

12 

5 

8 

12 

5 

9 

12 

5 

10 

12 

5 

11 

12 

5 

12 

12 

5 

Find  the  latitude  and  longitude  in,  and  the  course  and  distance 
made  good  by  inspection. 

Answers. 

T.  CO.  S.  11°  E.,  296  miles. 

D.  lat.  290.6  S.     Dep.  56.5  E.     Lat.  in,  43°  06'  N.     Mid.  lat. 
45°  31'.    D.  long.  81'  E.    Long,  in,  178°  35'  E. 


40 


Taylor's  MeoERN  Navigatiox. 


DAY'S  WORK. 


His. 

Coursfs. 

Knots. 

lOths 

Winds. 

Lee- 
way. 

Deviation. 

Remarks,  Etc. 

Pts. 

1 

South. 

7 

9 

E.S.E. 

3 

29°  E. 

Position     yesterday- 

2 

/ 

2 

noon,  lat.in,  48°10'S., 

3 

7 

2 

long,  in,  0°  10'  E. 

4 

7 

4 

5 

East. 

6 

2 

N.N.E. 

n 

10°  W. 

Var.  18°  20'  W. 

6 

5 

1 

7 

5 

2 

A   current    set   true 

8 

5 

2 

South    21    miles    from 

9 

5 

3 

the  time  the  departure 

10 

5 

was  taken  to  the  end  of 

11 

5 

the  day. 

12 

5 

1 

West. 

6 

s.s.w. 

5i 

14°  E. 

2 

6 

3 

6 

4 

6 

5 

5 

6 

5 

6 

North. 

6 

8 

E.N.E. 

1 

30°  W. 

7 

6 

/ 

8 

5 

6 

9 

5 

9 

10 

4 

7 

11 

5 

3 

12 

5 

Find  the  latitude  and  longitude  in,  and  the  course  and  distance 
made  good  by  inspection. 

Answers. 

Dep.  CO.  S.  44°  W.  29;  N.  87°  E.  42;  N.  32°  W.  31;  N.  60° 
W.  40;  South,  21. 

D.  lat.  6.6  N.  Dep.  29.2  W.  Lat.  in,  48°  3'  S.  D.  long.  44' 
W.    Long,  in,  0°  34'  W.    T.  co.  N.  78°  W.    Dist.  30  miles. 


1)ay"s    \Voi;k. 


41 


DAY'S  WORK. 


Hrs. 

Courses. 

Knots. 

lOths 

Winds. 

Lee- 
way. 

Deviation. 

Remarks,  Kte. 

Pts. 

1 

East. 

;; 

5 

N.N.E. 

2 

42° 

W. 

Cape  Charles 

2 

3 

5 

light-vessel,    in 

3 

3 

5 

lat.  37°  12'  N., 

4 

o 

5 

long.     75°     42' 

5 

3 

W.,     bore     by- 

6 

3 

compass    W.X 

7 

N.XE.iE. 

3 

2 

N.W. 

u 

23° 

W. 

N.,  distance  18 

8 

3 

2 

miles. 

9 

3 

4 

10 

3 

fi 

Ship's     head 

11 

3 

6 

East. 

12 

s.^w. 

3 

5 

E.S.E. 

^ 

5° 

E. 

1 

3 

5 

Dev.    as   per 

2 

3 

2 

log. 

3 

3 

2 

4 

3 

2 

Var.4°55'W. 

5 

3 

9 

6 

3 

2 

A  current  set 

7 

s.w.xs.^s. 

9 

6 

W.N.W. 

3i 

27° 

E. 

N.  1  E.    correct 

8 

1 

4 

magnetic         18 

9 

1 

miles  from  time 

10 

1 

departure     was 

11 

1 

taken  to  end  of 

12 

1 

day. 

Find  the  latitude  and  longitude  in.  and  the  course  and  distance 
made  good  by  inspection. 

A  ns  IV  CIS. 

Dep.  CO.  X.  54°  E.  18;  N.  Q6°  E.  20;  Xorth  IT;  S.  11°  W.  23; 
S.  14°  W.  8.     Current  co.  N.  2°  W.  18. 

D.  lat.  23.3.  Dep.  26.0.  D.  long.  33'  E.  Lat.  in.  37°  35'  N. 
Long,  in,  75°  09'  W.     T.  co.  X.  49°  E.     Dist.  35  miles. 


43 


Taylor's  Modern  Navigation. 


DAY'S  WORK. 


Hrs. 

Courses. 

Knots. 

lOths 

Winds. 

Lee- 
way. 

Deviation. 

Remarks,  Etc. 

1 

N.XE.fE. 

8 

5 

East. 

Pts. 

2| 

40"  E. 

A  point  in  lat. 

2 

8 

5 

20°  47'  S.,  long. 

3 

8 

5 

179°  59'  E.,  bore 

4 

8 

5 

by  compass   E.  | 

5 

S.XE. 

6 

E.XS. 

U 

27°  E. 

S^,    distance     12 

6 

4 

miles. 

7 

4 

8 

4 

Ship's  head  N. 

9 

W.|  N. 

5 

N.XW. 

3^ 

52°  E. 

E.|E. 

10 

6 

11 

7 

Dev.     as      per 

12 

8 

log. 

1 

East. 

12 

5 

N.N.E. 

i 

48°  W. 

2 

13 

5 

Var.  57°  W. 

3 

14 

5 

4 

14 

5 

A    current    set 

5 

S.S.E. 

16 

5 

8.W. 

0 

29°  E. 

correct  magnetic 

6 

16 

5 

S.  X  E.  1  E.     2| 

7 

16 

miles    per    hour 

8 

16 

from  the  time  the 

9 

W.XS.fS. 

5 

South. 

11 

49°  W. 

departure  was  ta- 

10 

2 

ken  to  the  end  of 

11 

2 

the  day. 

12 

1 

Find  the  latitude  and  longitude  in,  and  the  course  and  distance 
made  good  by  inspection. 


N. 

28^ 

W 

.  34 

;S 

.  27 

=  E. 

18; 

S. 

54° 

w 

E. 

65; 

S. 

16° 

E. 

10. 

Current 

CO 

S. 

77° 

Dep.  CO.  S.  81°  W.  12: 
26;  N.  12°  W.  55;  S.  51' 
E.  66. 

D.  lat.  14.7  S.  Dep.  65.5  E.  Lat.  in,  21°  02'  S.  D.  long.  70'  E. 
Long,  in,  178°  51'  W.    T.  co.  S.  77°  E.    Dist.  67  miles. 

In  this  example  the  longitude  will  be  greater  than  180°  after 
the  difference  of  longitude  is  applied,  so  we  must  subtract  it  from 
360°  to  get  the  desired  answer. 


Da.y's   Work. 


43 


DAY'S  WORK. 


Hrs. 

Ctmrses. 

Knots. 

... 

\Vin(l^^. 

wiiy. 

Doviatiou. 

Remarks,  Etc. 

ins. 

1 

N.E. 

14 

5 

N.N.W. 

24 

10°  w. 

No  Sima,  Japan, 

2 

14 

5 

in    lat.    34°  53'  N., 

3 

14 

long.    139°    54'   E., 

4 

13 

bore  bv  compass  N. 

5 

E.N.E. 

12 

5 

North. 

4i 

21°  W. 

W.,      distance      19 

6 

12 

miles. 

7 

12 

8 

12 

5 

Ship's  head  N.E. 

9 

East. 

13 

5 

North. 

3 

27°  W. 

10 

13 

5 

Dev.  as  per  log. 

11 

13 

5 

12 

13 

5 

Var.  6°  20'  E. 

1 

S.E. 

10 

5 

E.N.E. 

2i 

10°  E. 

2 

8 

A  current  set  cor- 

3 

7 

5 

rect  magnetic  E.N. 

4 

3 

E.  2:^  miles  per  hour 

5 

West. 

2 

S.S.W. 

6 

35^  E. 

from   the    time  the 

6 

1 

5 

departure  was  taken 

7 

1 

3 

to    the   end   of   the 

8 

2 

2 

day. 

9 

N.W. 

3 

6 

N.N.E. 

^ 

25°  E. 

10 

3 

8 

11 

3 

8 

12 

2 

8 

Find  the  latitude  and  longitude  in,  and  the  course  and  distance 
made  good  by  inspection. 

Answers. 

Dep.  CO.  S.  49°  E.  19;  N.  69°  E.  56;  S.  79°  E.  49;  S.  77°  E. 
54;  S.  3°  E.  29;  N.  19°  E.  7;  N.  19°  W.  14.  Current  co.  N.  74° 
E.  54. 

D.  lat.  8.1  S.  Dep.  218.4  E.  Lat.  in,  34°  45'  N.  D.  long.  4° 
27'  E.    Long,  in,  144°  21'  E.    T.  co.  S.  88°  E.    Dist.  219  miles. 


DIVISION  II. 

THE  SAILINGS. 

The  tables  required  to  work  the  problems  contained  in  this  sec- 
tion of  the  book  are  Table  3,  Meridional  Parts;  Table  43,  Loga- 
rithms of  Numbers;  and  Table  44,  Log.  Sines,  Tangents,  and 
Secants.  So,  before  proceeding  with  the  problems  themselves,  it 
will  not  be  amiss  to  explain  the  use  of  the  above  tables. 

For  the  sake  of  illustration,  suppose  we  wish  to  find  the  Meridi- 
onal Parts  for  59°  27'. 

First  turn  up  Table  3  and  look  along  the  head  or  foot  of  the 
pages  until  the  required  number  of  degrees  is  found,  namely,  59° ; 
then  under  the  59°  and  abreast  of  the  27'  (which  we  look  for  on 
the  side)  will  be  found  4442'.!. 

Example. — Eequired  the  Mer.  Parts  corresponding  to  37°  19'. 
Ans.  2402'.6. 

Note. — The  foregoing  is  required  in  the  first  part  of  Mercator's 
Sailing. 

To  Use  Tasle  42,  Logarithms  of  Numbers. 

The  index  of  a  number  is  one  less  than  the  number  of  figures; 
for  example,  if  the  number  contain  two  figures,  the  index  is  1 ; 
if  three  figures,  the  index  is  2 ;  if  four  figures,  the  index  is  3,  and 
so  on.  Therefore,  before  entering  the  table,  mark  down  the  index, 
with  the  decimal  to  the  right.  If  you  look  at  the  first  part  of  the 
table  when  it  begins  at  one  figure,  you  will  notice  that  when  there 
is  one  figure  there  is  a  0  for  the  index,  but  when  there  are  two 
figures  there  is  1  for  the  index,  and  abreast  of  100  there  is  2.  of 
an  index;  after  this  you  are  supposed  to  know  how  to  find  the  index 
yourself,  according  to  the  rule  given  above. 

Example. — Eequired  the  log.  corresponding  to  4976. 
Here  we  have   four   figures,   so  the   index   is  three,   expressed 
thus,  3.    Then  search  for  the  first  three  figures  on  the  left,  namely, 
497,  and  abreast  of  them,  under  the  fourth  figure,  which  is  6,  take 
out  the  log.  and  mark  it  down;  thus,  3.69688. 
Example. — Eequired  the  log.  for  293. 

Here  there  are  three  figures  only,  so  abreast  of  the  number  293, 
in  the  first  column,  you  will  find  2.46687,  to  which  you  must  prefix 
the  figure  2,  because  2  is  the  index  of  three  figures.  If  the  number 
consist  of  more  than  four  figures,  proceed  by  the  rule  given  on  pages 
184-185,  Bowditch  Epitome,  edition  of  1903. 


Sailings.  45 


After  learning  the  foregoing  the  student  must  next  understand 
how  to  take  out  of  Table  42  a  number  corresponding  to  a  given 
logarithm. 

Example. — Find  tlie  number  corresponding  to  log.  2.58070. 

Here  you  must  search  in  the  body  of  the  table  until  the  number 
58070  is  found,  then  note  the  figures  to  the  left  and  the  figure  on 
top  of  the  column;  in  this  case  it  will  be  found  abreast  of  380  and 
under  the  8 ;  mark  down  all  four  and  point  ofE  one  figure,  namely, 
the  8,  because  there  are  two  in  the  index,  for  the  reason  that  the 
number  found  must  always  be  one  more  than  the  index  of  the  log. 
The  answer  will  then  be  380.8.  If  tihere  be  only  one  for  index,  then 
point  off  two  figures;  thus,  38.08.  If  only  a  cipher,  then  point  off 
three;  thus.  3.808.  But  if  there  be  three  for  index,  then  place  the 
point  to  the  right  of  all  four,  and  the  answer  will  be  3808.  of  a 
v\-hole  number. 

To  Use  Table  44,  Log.  Sines,  Tangents,  and  Secants. 

When  entering  this  table  to  take  out  a  log.,  there  are  two  ways 
of  reading  it ;  namely,  from  the  top  and  from  the  bottom. 

If  you  read  degrees  on  the  top.  read  the  names  on  the  top,  and 
minutes  from  the  same  side,  under  the  degrees;  but  if  you  read 
degrees  from  the  bottom,  read  the  names  from  the  bottom,  and 
minutes  above  the  degrees. 

Example. — Eequired  the  log.  sine  of  30°  27'. 

Look  on  to])  of  page  for  the  30°,  then  under  the  30°  look  for 
the  27',  and  take  out  the  log.  from  the  sine  column  abreast,  which 
is  9.70482. 

E.vample. — Required  tlie  log.  tangent  of  67°  55'. 

Here  we  must  look  for  the  degrees  on  the  bottom  of  the  page, 
because  they  are  more  than  45°,  and  when  found,  run  up  the  minute 
column  until  we  see  55',  then  abreast  of  it,  and  in  the  tangent 
column,  reading  from  the  bottom,  we  find  the  log.  10.39177. 

Example. — Required  the  log.  cosecant  of  112°  45'. 
Look  for  112°  on  the  bottom  of  page  and  for  the  45'  above  it. 
Abreast  of  the  45°  will  be  found,  in  the  cosecant  column,  10.03517. 


46  Taylor's  Modern  Navigation. 


To  Find  the  Degrees  and  Minutes  Corresponding  to  a  Log. — 
Search  in  the  required  column  until  the  log.  is  found,  and  note 
the  degrees  on  the  top  and  the  minutes  to  the  left  if  the  name  is 
taken  from  the  top,  but  if  the  name  is  taken  from  the  bottom,  read 
the  degrees  from  the  bottom,  and  the  minutes  to  the  right. 

Example. — Eequired  the  degrees  and  minutes  corresponding  to 
log.  tangent  10.47213. 

Here  we  search  in  tangent  column,  looking  from  the  bottom 
whenever  the  index  of  log.  tangent  is  10.  or  more,  and  from  the 
top  when  the  index  is  9.  or  less.  We  find  in  this  example  the  log. 
abreast  of  22'  on  the  71°  page,  so  we  mark  down  71°  22'. 

Note. — It  is  unnecessary  in  the  sailings  to  work  logs,  to  seconds, 
but  it  is  in  some  of  the  higher  problems,  and  will  be  explained 
when  necessary. 

MERCATOR'S  SAILING. 

Mercator's  sailing  is  the  method  used  to  find  the  true  course  and 
distance  between  two  places  when  the  latitude  and  longitude  are 
known.  For  the  theory  of  this  problem,  see  page  49,  articles  124 
and  125,  also  page  19,  article  63,  Bowditch  Epitome,  edition  of 
1902. 

Rule. 

Mark  down  the  latitudes  and  longitudes  under  each  other,  as  seen 
in  the  example. 

Find  the  difference  of  latitude  by  adding  the  latitudes  together 
if  they  are  of  different  names,  and  by  subtracting  if  the  same  name. 
Bring  the  sum,  or  remainder,  into  minutes  by  multiplying  by  60. 
The  result  will  be  the  diff.  of  kit.  in  minutes. 

Next  find  the  difference  of  longitude  by  adding  the  longitudes- 
together  if  they  are  of  different  names,  and  by  subtracting  if  the- 
same  name.  Bring  the  sum,  or  remainder,  into  minutes  by  multi- 
plying by  60.     The  result  will  be  the  diff.  of  long,  in  minutes. 

To  Find  the  Meridional  Difference  of  Latitude. — Take  out  of 
Table  3  the  Mer.  Parts  for  both  latitudes.  Thus,  look  on  the  top 
of  the  page  for  the  degrees,  and  on  the  sides  for  the  minutes.  Run 
your  finger  across  from  the  minutes,  and  under  the  degrees  will  be- 


Sailings. 


47 


found  the  Mer.  Parts.  Mark  these  Mer.  Parts  under  each  other, 
and  add  or  subtract  them,  according  as  you  add  or  subtract  the 
latitudes.    The  result  will  be  the  mer.  diff  of  lat. 

To  Find  the  Course. — Mark  down  the  diff.  of  long,  and  under  it 
the  mer.  diff.  of  lat.,  always  adding  10  to  the  index  of* the  diff.  of 
long.  Take  out  of  Table  43  the  log.  of  the  diff.  of  long.,  always 
subtraeting  from  it  the  log.  of  the  mer.  diff.  of  lat.  Now  look  for 
the  remainder  in  the  tangent  column  of  Table  44,  and  when  found, 
note  the  degrees  on  the  top  and  the  minutes  to  the  left,  if  you  read 
tangent  from  the  top ;  but  if  you  read  tangent  from  the  bottom,  note 
the  degrees  at  the  bottom  and  the  minutes  to  the  right.  In  either 
case  the  degrees  and  minutes  will  be  the  course. 

To  Name  the  Course. 


From  a 

S. 

lat. 

to  a                 N. 

lat. 

the  course  is  N. 

From  a 

N. 

lat. 

to  a                S. 

lat. 

the  course  is  S. 

From  a 

N. 

lat. 

to  a  greater  N. 

lat. 

the  course  is  N. 

From  a 

N. 

lat. 

to  a  smaller  X. 

lat. 

the  course  is  S. 

From  a 

S. 

lat. 

to  a  greater  S. 

lat. 

the  course  is  S. 

From  a 

S. 

lat. 

to  a  smaller  S. 

lat. 

the  course  is  N. 

From  a 

w 

long. 

to  an              E. 

long. 

the  course  is  E. 

From  an 

E. 

long. 

to  a                 W 

long 

the  course  is  W 

From  an 

E. 

long. 

to  a  greater  E. 

long. 

the  course  is  E. 

From  an 

E. 

long. 

to  a  smaller  E. 

long. 

the  course  is  W 

From    a 

W 

long. 

to  a  greater  W 

long. 

the  course  is  W 

From     a 

W 

long. 

to  a  smaller  \\ 

long. 

the  course  is  E. 

If  the  sum  of  the  two  longitudes  be  greater  than  180°,  subtract 
it  from  360°  and  reduce  the  remainder  to  minutes.  The  result 
■will  be  the  diff.  of  long.  In  this  case,  name  the  course  the  same 
name  as  the  longitude  from. 

To  Find  the  Distance.— Take  out  of  Table  44  the  secant  of  the 
,course  and  add  the  log.  (Table  42)  of  the  diff.  of  lat.  to  it.  The 
.sum,  rejecting  10  from  the  index,  will  be  the  log.  of  the  distance 
(Table  42). 

The  number  of  figures  required  in  the  distance  will  always  be 
•one  more  than  the  index  of  the  sum  of  the  logs. ;  that  is,  if  the  in- 
dex is  1,  two  figures  will  be  required;  if  2,  three  figures;  if  3,  four 
:figures,  etc. 


48  •  Taylor's  Moderj^  Xavigatiox. 


Lat.  A,  38°  00'  N. 
Lat.  B,  34    29  N. 

2454.1 
2193.6 

3    31 

Mer.  Part,  260.5 

60 
Diff.oflat.  211 

Examples. 
(Tables  required:     Meridional  Parts,  Table  3;  Common  Loga- 
rithms, Table  42;  Log.  Sines,  Tangents,  and  Secants,  Table  44.) 

Example. — Find  the  course  and  distance  from  A  to  B. 

Long.  18°  15'  E. 
Long.  20  40  W. 

38  55 
60 

Diff.  of  long.  2335 
To  Find  the  Course. 

Log.  of  diff.  of  long.  2335    =13.36829  (Subtract  always.) 
Log.  of  Mer.  Parts,     260.5=  2.41581 

Tangent,  10.95248  Course  S.  83°  38'  W. 

To  Find  the  Distance. 

Secant  of  course,  83°  38'    =     .95510  (Add  always.) 
Log.  of  diff.  of  lat.     211     =  2.32428 

Log.  of  distance,  3.27938  Dist.  1903  miles. 

The  index  of  the  diff.  of  long,  is  3,  but  as  10  must  always  be 
added  to  the  index  of  diff.  of  long.,  the  index  must  be  13.  The  in- 
dex of  the  Mer.  Parts  is  2,  because  there  are  only  three  whole 
numbers  in  it.  When  looking  for  the  tangent  in  the  question,  you 
must  read  from  the  bottom  of  the  page  and  note  the  minutes  to  the 
right;  the  secant  is  found  abreast  of  the  tangent.  The  log.  of  the 
distance  is  found  abreast  of  190  and  under  3. 

To  Name  the  Course. — From  North  to  less  North  latitude  the 
course  is  South ;  from  East  to  West,  the  course  is  West. 

Example. — Find  the  course  and  distance  from  A  to  B. 

1112.1  Long.  178°  12'  E. 

674.9  Long.  168    12  \\\ 

Mer.  Part,  1787.0  316    24 

360    00 


Lat. 

A, 

18° 

20' 

N. 

Lat. 

B, 

11 

29 
60 

15 
35 

S. 

Diff.  of  lat. 

1775 

13°  36' 
60 


Diff.  of  long.  816 


Sailings.  4J> 


To  Find  the  Course. 

Log.  of  diff.  of  long.  816    -=12.91169  (Subtract  always.) 
Log.  of  Mer.  Parts,  1787.0=  3.25212 

Tangent,  9.65957  Course  S.  24°  33'  E. 

To  Find  the  Distance. 

Secant  of  course,  24°  33'=   .04115    (Add  always.) 
Log.  of  diff.  of  lat.  1775  =3.24920 

Log.  of  distance,  3.29035  Dist.  1952  miles. 

In  this  case  the  sum  of  the  longitudes  is  greater  th<\n  ISO"^,  and 
therefore  must  be  subtracted  from  360°  and  the  remainder  reduced 
to  minutes.  When  this  occurs,  name  the  course  the  same  name  as 
the  first  longitude  or  longitude  from. 

The  number  of  figures  required  in  the  distance  is  always  one  more 
than  the  index  calls  for. 

Examples  for  Practice. 
Xo.  1. 
Find  the  course  and  distance  from  Point  Eeycs.  in  latitude  38° 
00'  jST.,  long.  123°  0'  W.,  to  No  Sima,  Japan,  in  latitude  34°  53' 
N.,  long.  139°  54'  E. 

From  lat.  38°   00'  N".  Long.  123°   00'  W. 

To        lat.  34°   53'  X.  Long.  139°   54'    E. 

Answer.— D.  lat.  187';  mer.  D.  lat.  231.5;  D.  long.  5826';  tan- 
gent 11.40082;  T.  co.  S.  87°  43'  W.;  log.  of  dist.  3.67151;  dist. 
4694  miles. 

No.  2. 

Find  the  course  and  distance  from  Cape  Beale  to  Cape  Arago. 

From  lat.  48°  48'  N.  Long.  12-5°  14'  W. 

To       lat.  43°  21'  N.  Long.  124°  23'  W. 

Answer.— D.  lat.  327';  mer.  D.  lat.  470.4;  D.  long.  51';  tangent 

9.03510;  T.  co.  S.  6°  12'  E.;  log.  of  dist.  2.51710;  dist.  328.9  miles. 

No.  3. 
Find  the  course  and  distance  from  Honolulu  to  Auckland. 
From  lat.  21°  18'  N.  Long.  157°   52'  W. 

To        lat.  36°  50'  S.  Long.  174°  49'    E. 

Answer.— D.  lat.  3488' ;  mer.  D.  lat.  3666.6 ;  D.  long.  1639 ;  tan- 
gent 9.65027;  T.  co.  S.  24°  5'  W.;  log.  of  dist.  3.58213;  dist.  3821 
miles. 

Taylor's    Mod.   Nav.   4. 


50  Taylor's  Modern  Navigation. 


No.  4. 
Find  the  course  and  distance  from  Auckland  to  Sydney. 
From-  lat.  36°  50'  S.  Long.  174°  49'  E. 

To        lat.  33°  50'  S.  Long.  151°  18'  E. 

Answer.— D.  lat.  180';  mer.  D.  lat.  219.7;  D.  long.  1411';  tan- 
gent 10.80770;  T.  co.  N.  81°  9'  W.;  log.  of  dist.  3.06818;  dist.  1170 
miles. 

No.  5. 
Find  the  course  and  distance  from  Auckland  to  Cape  Horn. 
From  lat.  36°  50'  S.  Long.  174°  49'    E. 

To        lat.  55°  59'  S.  Long.     67°  16'  W. 

Answer.— D.  lat.  1149';  mer.  D.  lat.  1686.7;  D.  long.  7075';  tan- 
gent 10.62261;  T.  co.  S.  76°  35'  E.;  log.  of  dist.  3.69477;  dist. 
4952  miles. 

No.  6. 
Find  the  course  and  distance  from  Cape  Horn  to  St.  Helena. 
From  lat.  55°  59'  S.  Long.  67°  16'  W. 

To       lat.  15°  55'  S.  Long.     5°  44'  W. 

Answer.— D.  lat.  2404;  mer.  D.  lat.  3091.9;  D.  long.  3692;  tan- 
gent 10.07702;  T.  co.  N.  50°  3'  E.;  log.  of  dist.  3.57331;  dist.  3744 
miles. 

No.  7. 
From  lat.  12°     4'  S.  Long.  77°  16'  W. 

To        lat.  20°  13'  S.  Long.  70°  12'  W. 

Answer.— Tangent  9.92236;  T.  co.  S.  39°  54'  E. ;  log.  of  dist. 
2.80442 ;  dist.  637  miles. 

No.  8. 
From  lat.  17°  42'  S.  Long.  71°  23'  W. 

To        lat.  20°  12'  S.  Long.  70°  11'  W. 

Answer.— Tangent  9.65867;  T.  co.  S.  24°  30'  E.;  log.  of  dist 
2.21707;  dist.  164.9  miles. 

No.  9. 
From  lat.  56°  17'  N.  Long.  176°  59'  E. 

To        lat.  40°  18'  S.  Long.  101°  50'  E. 

Answer.— Tangent  9.82690;  T.  co.  S.  33°  52'  W.;  log.  of  dist. 
3.84380;  dist.  6980  miles. 


Sailings.  51 


Xo.  10. 
From  lat.  60°  27'  S.  Long.  179°  59'  W. 

To        lat.     1°  15'  S.  Long.  179°  20'    E. 

Answer.— T.  co.  N.  00°  32'  W.;  dist.  3552  miles. 

Xo.  11. 
From  lat.     0°     2'  X.  Long.  153°  40'  W. 

To        lat.  10°   15'  S.  Long.  153°  40'    E. 

Answer.— T.  eo.  S.  78°  59'  W.;  dist.  3224  miles. 

Xo.  12. 
From  lat.  38°  50'  X.  Long.  50°  38'  E. 

To        lat.  00°  00'  Long.  00°  00' 

Answer.- T.  co.  S.  50°  21'  W.;  dist.  3G51  miles. 

Xo.  13. 

From  lat.  75°  15'  S.  Long.  108°  22'    E. 

To        lat.  42°  59'  S.  Long.     10°  20'  W. 

Answer.— T.  co.  X.  59°  43'  W.;  dist.  3839  miles. 

Xo.  14. 
From  lat.  25°   16'  X.  Long.  00°  20'    E. 

To        lat.  48°  18'  X.  Long.  15°  29'  W. 

Answer.— To.  co.  X.  28°  33'  W.;  dist.  1573  miles. 

Xo.  15. 
From  lat.  58°   58'  X.  Long.   75°   40'   W. 

To       lat.  40°   15'  X.  Long.     0°     2'   E. 

Answer.— T.  co.  S.  68°  50'  E.;  dist.  3110  miles. 

Xo.  16. 
From  lat.  10°  16'  S.  Long.  88°  51'  W. 

To        lat.  17°  20'  X.  Long.  40°  50'  W. 

Answer.— T.  co.  X.  59°  57'  E.;  dist.  3310  miles. 

PAEALLEL  SAILIXG. 

To  Find  the  Distance  Between  Two  Places  ^Yhen  Their  Latitudes 
Are  the  Same. 

EULE. 

To  the  cosine  of  the  latitude  add  the  log.  of  the  diff.  of  long.  The 
sum,  rejecting  the  10  in  the  index,  will  be  the  log.  of  the  distance. 


52  Taylor's  Modern  Navigation. 

Exantples. 
From  lat.  38°  00'  X.  Long.  123°  00'  W. 

To       lat.  3S°  00'  X.  Long    179     59    W. 

56°   59' 
60 
3419 

Cosine  of  lat.         38°  00'  N. -9.89653 
Log.  of  diff.  of  long.        3419  =3.53390 

3.43043  =  2694  miles. 

Lat.   10°   12'  X.  Long.  45°   50'  E. 

Lat.  10°  12'  X.  Long.  18°  20'  E. 

List.  1624  miles. 

Lat.  27°  52'  X.  Long.  89°  10'  W. 

Lat.  27°   52'  X.  Long.  20°   15'    E. 

Dist.  5804  miles. 

Lat.  34°     5'  S.  Long.  100°   10'  W. 

Lat.  34°     5'  S.  Long.     74°  45'  W. 

Dist.  1263  miles. 

Lat.  12°  16'  S.  Long.  176°  21'    E. 

Lat.  12°  16'  S.  Long.  176°  21'  W. 

Dist.  428.0  miles. 

MERCATOK'S  SAILIXG  BY  IXSPECTIOX   (SHORT 
METHOD). 

Find  the  diff.  of  lat..  mer.  diff.  of  lat.,  and  diff.  of  long,  as  in 
the  longer  method.  Point  off  to  the  right  one  figure  of  each,  making 
them  small  enough  to  enter  the  tables. 

With  a  tenth  part  of  the  mer.  diff.  of  lat.  as  lat.,  and  a  tenth  part 
of  the  diff.  of  long,  as  dep.,  enter  Table  2  and  search  for  them  in 
their  own  columns  until  they  are  found  alongside  of  each  other. 
When  found,  note  the  degrees  on  top  of  page  if  lat.  is  the  greater, 
and  on  bottom  if  dep.  is  the  greater.  The  result  will  be  the 
course,  to  be  named  by  the  same  rule  as  in  the  longer  method. 


Sailings.  53 


To  Find  iJic  Dlstanvc. —  Kcej)  on  ^ame  page  and  search  in  the 
lat.  column  for  one  tenth  j)art  of  the  proper  clifE.  of  lat..  and  when 
found,  note  the  distance  al)reast  in  the  distance  column,  annex  a 
cipher  to  it.  and  the  result  will  he  the  distance. 

If  a  tenth  part  of  the  element  recpiired  is  too  large  for  the  tal)le, 
take  one  half  or  one  third,  and  enter  the  tables  as  before;  but 
when  finding  the  distance,  multiply  the  result  by  whatever  figure 
was  used  to  reduce  the  elements. 

This  method  is  correct  for  short  distances  only,  and  should  be 
used  only  for  finding  the  distance  between  position  of  one  day  and 
the  next. 

Thus,  suppose  diff.  of  lat.  to  be  129'  ^.,  nier.  diff.  of  lat.  140', 
and  diff.  of  long.  89'  W.     Find  course  and  distance  by  inspection. 

The  diff.  of  long.,  8.1),  in  de}).  column,   }    ^-  ,  ^  ^    roo  ly 
Mer.  diff.  of  lat.,  14.0,  in  lat.  column,   S   ^       ^  ' 

and  12.9,  in  lat.  column,  gives  24,  in  the  distance  column  abreast, 
wdiich,  multiplied  by  10,  gives  240  miles. 

TO     FIND     THE     DIFFEKEXCE     OF     LONGITUDE     BY 
PAEALLEL    SAILING. 

This  method  may  Ije  put  to  ]iractical  use  when  finding  the  diff. 
of  long,  in  day's  work. 

Rule. 
Take  the  secant  of  the  middle  latitude  from  Taljle  44  and  add 
the  log.,  Table  42,  of  the  departure  to  it.     The  sum.  rejecting  the 
10  from  the  index,  will  be  the  log.  of  the  diff.  of  long..  Table  42. 

Example.— lA\t.  49°  54'  N.,  dep.  134.G.  Required  the  diff.  of 
long. 

Secant  of  lat.  49°  54' =  10.19103 
Log.  of  dep.       134.6  =  2.12905 

2.32008=209.0  diff.  of  long. 

We  found  the  sum  (nearly)  of  these  logs,  abreast  of  209,  and 
under  0,  therefore  we  mark  down  2090;  and  because  the  index  is  2, 
we  must  have  three  figures  in  the  answer,  therefore  we  put  the  deci- 
mal point  before  the  last  figure  and  get  209.0,  which  is  the  diff.  of 
long. 


54:  Taylor's  Modern  Xavigation. 


Examples  for  Practice. 

Lat.  2°  27'  S.;  dep.  59.6.     Required  the  diff.  of  long. 
Answer. — 59.66. 


Lat.  19°  51'  N.;  dep.  181.6.    Required  the  diff.  of  long. 
Answer. — 193.1. 

Lat.  19°  51'  X.;  dep.  320.5.    Required  the  diff.  of  long. 
Answer.— 340.8. 

Lat.  82°  10'  S.;  dep.  10.9.     Required  the  diff.  of  long. 
Answer.— 79.98. 

MIDDLE-LATITUDE  SAILING. 

(Extract  from  Lieutenant  Raper's  Epitome  of  Navigation,  pages 
103,  104.) 

(This  valuable  book  should  be  in  the  lil)rary  of  every  navigator, 
or  those  interested  in  navigation.) 

"The  diff.  of  long,  found  by  mid.  lat.  is  true  at  the  Equator, 
and  very  nearly  true  for  short  distances  in  all  latitudes,  especially 
when  the  course  is  nearly  East  or  West.  In  hig*h  latitudes,  when 
the  distance  is  great  and  the  course  oblique,  the  error  becomes 
considerable,  but  the  result  may  be  made  as  accurate  as  we  please 
by  subdi-^iding  the  distance  run  into  small  portions  and  finding 
the  diff.  of  long,  for  each  portion  separately. 

"The  diff.  of  long,  deduced  by  mid.  lat.  sailing  is  too  small;  an 
estimate  of  the  error  for  places  on  the  same  side  of  the  Equator 
may  be  formed  with  the  help  of  a  few  cases.  Suppose  the  course  4 
points,  or  45°,  and  the  D.  lat.  10°,  or  600  miles;  then  if  this  D. 
lat.  is  made  good  in  any  lat.  below  30°,  the  error  of  the  D.  long,  will 
not  exceed  2';  if  made  good  between  the  parallels  of  40°  and  50°, 
the  error  will  be  about  3';  and  between  60°  and  70°,  about  19',  or 
one  third  of  a  degree.  For  smaller  distances  the  errors  will  be 
much  less,  and  for  greater  distances  much  greater,  as  they  vary 
in  much  more  rapid  proportion  than  the  distances. 

"It  is  proper  to  remark  that  when  the  course  is  large,  that  is, 
nearly  seven  or  eight  points,  the  diff.  of  long,  should  be  found  by 
mid.  lat.  in  preference  to  Mercator's  sailing;  because,  although  the 
latter  is  mathematically  correct  in  principle,  yet  a  small  error  in 
the  course  may,  when  the  course  is  large,  produce  a  considerable 
error  in  the  diff.  of  long. 


Sailings.  55 


"The  reason  of  this  is  easily  shown.  In  mid.  lat.  sailing  we 
convert  the  departure  into  D.  long.  The  process  increases  the 
dep.  in  a  proportion  which  is  less  than  2  to  1  in  all  latitudes  below 
60°,  and  exceeds  3  to  1  in  latitudes  beyond  70°.  The  error  of  the 
dep.,  increased  in  the  same  proportion,  becomes  thus  the  error  of 
the  D.  long.  Now,  when  the  course  is  nearly  East  or  West,  the 
dep.  is  nearly  the  same  as  the  distance,  and  an  error  of  some  de- 
grees in  the  course  does  not  affect  the  dep.  sensibly ;  hence  in  this 
case  the  error  of  the  D.  long,  depends  on  that  of  the  dist.  alone. 

"But  in  Mercator's  sailing,  on  the  other  hand,  we  convert  the 
Mer.  diff.  of  lat.  into  diff.  of  long.,  and  the  process,  when  the 
course  is  large,  converts  a  given  Mer.  diff.  of  lat.  into  diff.  of  long, 
much  greater  than  itself;  and  thus  increases  the  error  of  the  Mer. 
diff.  of  lat.  in  the  same  proportion.  Thus,  for  example,  at  the 
course  80°  the  D.  of  long,  exceeds  the  Mer.  diff.  of  lat.  in  the  pro- 
portion of  6  to  1;  at  the  course  85°  this  proportion  is  11  to  1. 
Now,  when  the  course  is  large  a  slight  change  in  it  sensibly  affects 
the  D.  lat.,  and  also  the  Mer.  diff.  of  lat.,  which  is  deduced  directly 
from  it. 

"In  high  latitudes  the  Mer.  Parts  vary  rapidly,  and  the  error  of 
the  D.  long,  is  aggravated  accordingly;  hence  the  precept  more 
especially  demands  attention  in  high  latitudes." 

Middle  Latitude  Sailing  is  a  method  to  find  the  true  course 
and  distance  betwei'n  two  places  when  both  latitude  and  longitude 
are  given. 

There  are  quite  a  number  of  different  cases,  but  only  one  will  be 
given  here,  as  it  will  be  sufficient  for  the  ordinary  practice  of  navi- 
gation. 

The  method  is  not  exact  in  all  cases,  but  may  be  used  with  abso- 
lute confidence  when  the  distance  is  small  and  the  ship  is  in  a 
high  latitude,  also  when  latitudes  have  same  name,  and  for  larger 
distances  if  the  latitude  is  low  and  the  course  greater  than  45°, — 
the  nearer  90°,  the  better.  If  the  latitudes  have  different  names, 
the  two  portions  of  the  track  on  the  opposite  sides  of  the  Equator 
should  be  calculated  separately. 

Rule. 
Mark  down  on  the  left-hand  side  of  the  page  the  two  latitudes 
under  each  other,  and  a  little  to  the  right  mark  down  the  same  lati- 
tudes again,  and  on  the  right-hand  side  of  page  mark  down  the  two 
longitudes  as  seen  in  the  examples. 


56  Taylor's  Moderx  Xavigation. 


To  Find  the  Difference  of  Latitude. — If  the  latitudes  have  the 
same  name,  subtract  the  lesser  from  the  greater;  but  if  different 
names,  add  and  bring  the  result  into  minutes  by  multiplying  by  60. 

To  Find  Middle  Latitude. — If  latitudes  have  same  name,  one 
half  the  sum  will  be  the  mid.  lat.,  but  if  different  names,  and  are 
nearly  equal,  one  half  the  greater  lat.  will  be  the  mid.  lat. ;  then 
multiply  by  60  to  obtain  the  minutes. 

These  rules  may  be  assumed  to  be  correct  for  short  distances  and 
for  ordinary  purposes,  but  they  are  not  really  so,  since  the  true  mid. 
lat.  will  always  be  a  little  nearer  to  the  Pole. 

There  is  a  table  given  in  the  Bowditch  Epitome,  computed  by 
Workman  in  1805,  whereby  the  true  mid.  lat.  may  be  found,  but 
it  is  not  necessary  unless  great  accuracy  is  required. 

To  Find  the  Difference  of  Longitude. — If  longitudes  have  same 
names,  subtract  the  lesser  from  the  greater;  but  if  different  names, 
add,  and  bring  the  result  into  minutes  by  multiplyiug  by  60.  The 
computation  will  then  be  as  follows : 

To  Find  the  Course. — To  the  log.  of  the  diff.  of  long,  add  cosine 
of  mid.  lat.  and  suijtract  from  the  sum  the  log.  of  the  diff.  of  lat. 
The  remainder  will  be  the  tangent  of  the  course.  iSTame  the 
course  by  same  rule  as  in  Mercators  sailing. 

To  Find  Distance. — To  the  secant  of  the  course  add  the  log.  of 
diff.  of  lat.  The  sum.  rejecting  10  from  the  index,  will  be  the  log. 
of  the  distance. 

Example. — Find  the  true  course  and  distance  from  A  to  B  by 
middle-latitude  sailing. 


Lat.  A,  20°  38'  N. 

20°  38' 

N. 

Long. 

A, 

156°  22'  W 

Lat.  B,  27  06  N. 

27  06 

N. 

Long. 

B, 

142  11  E. 

6  28 

2)47  44 

"298""33 

60 

Diff.  of  lat.  388 

Mid. 

lat.  23°  52' 

360  00 

61  27 
60 

Diff.  of  long.  368^ 


Sailings.  57 


To  Find  the  Course. 

To  log.  of  diff.  of  long.         3687'=  3.56667 
Add  cosine  mid.  lat.         23°  52'=  9.96118 

From  sum,  13.52785 

Subtract  log.  diff.  of  lat.        388'=  2.58883 

Gives  log.  tangent  of  course,  N.  83°  26'  W.  =  10.93902 

To  secant  of  course,  X.  83°  26' W.  =  10.94173 
Add  log.  D.  lat.  388'=  2.58883 

Log.  of  dist.  3.53056  =  3393  miles. 

Answer.— N.  83°  26'  W.     Dist.  3393  miles. 

Example. — Find  the  true  course  and  distance  from  A  to  B  by 
middle  latitude  sailing. 


Lat.  A,  38°  00'  N.                38°  00'  N.               Long.  A, 
Lat.  B,  34    29   N.                34    29  N.               Long.  B, 

,  18°  15'  E. 
,  20    40  W, 

3    31                   2)72    29 

60                                

_I1           Mid.  lat.  36°  14' 

D.  lat.    211                                                             D.  long. 

Log.  I),  long.                         2335'=  3.36829 
+  Cosine  mid.  lat.                 36°  14'=  9.90667 

38    55 
60 

2335 

Sum,                                                   13.27496 
-Log.  D.  lat.                             211'=  2.32428 

-Tangent  of  course,  S.  83°  36'  W.  =  10.95068 

Secant  co.                S.  83°  36'  W.  =  10.95285 
+  Log.  D.  lat.                             211'=  2.32428 

Log  of  dist.                                          3.27713  = 
Answer.— S.  83°  36'  W.    Dist.  1893  Miles. 

=  1893  miles. 

GREAT-CIRCLE  SAILIXG. 

A  great  circle  is  an  imaginary  line  drawn  around  the  world. 
which,  if  the  world  were  cut  through  on  this  line,  woulil  divide  it 
into  two  equal  parts,  the  knife  passing  through  the  center.  It  is  gen- 
erally defined  thus :  A  great  circle  is  a  circle  whose  plane  passes 
through  the  center  of  any  sphere. 

All  true  meridians  are  great  circles;  so,  also,  is  the  Equator  a 
great  circle. 


58  Taylor's  ]\Iodern  Xavigatiox. 


The  preceding  methods,  namely,  Mercator's  and  middle  lati- 
tude sailing,  give  the  true  course  and  the  distance  from  one  place 
to  another,  but  this  is  not  the  shortest  distance,  although  if  you 
steer  on  this  course  it  will  eventually  bring  you  to  your  destination. 
By  plotting  the  course  by  Mercator's  or  middle-latitude  sailing  on 
a  Mercator's  chart,  it  will  be  noticed  that  the  course  makes  the 
same  angle  with  each  meridian  it  crosses;  but  if  you  go  to  a  globe 
and  stretch  a  thread  between  two  places,  like  San  Francisco  and 
Yokohama,  Japan,  it  will  be  seen  that  the  thread  cuts  each  true 
meridian  at  a  different  angle.  It  is  therefore  very  evident  that  the 
Mercator  or  the  middle-latitude  course  will  not  take  you  the 
shortest  distance,  for  the  reason,  as  before  remarked,  that  the  course 
is  always  the  same,  whereas  on  the  great  circle  the  course  is  always 
changing. 

If  the  course  between  two  places  is  Xorth  or  South,  or  if  both 
places  are  on  the  Equator,  where  the  course  would  be  East  or  West, 
it  is  obviously  unnecessary  to  consider  the  problem  of  great-circle 
sailing,  as,  under  such  circumstances,  we  should  be  sailing  on  the 
Equator  or  on  a  true  meridian,  which  are  both  great  circles. 

The  computation  of  the  problem  is  a  very  lengthy  one,  and  is 
rarely  used.  It  involves  the  calculation  of  the  Vertex,  maximum 
separation  of  the  latitude,  etc.,  but  the  United  States  Hydrographic 
Office  comes  to  the  rescue  of  the  navigator  by  publishing  the  Great 
Circle  or  Gnomonic  Chart. 

On  the  monthly  Pilot  Charts  (which  may  be  obtained  free  of 
charge  from  the  local  Hydrographic  officials)  the  principal  great- 
circle  tracks  are  printed,  but  if  the  one  desired  is  not  found  thereon, 
recourse  must  be  had  to  the  Great  Circle  Chart  itself. 

EULE. 

Lay  a  straight-edge  over  the  two  places  and  draw  a  straight  line, 
and  mark  off  the  latitude  for  every  five  degrees  of  longitude,  trans- 
fer these  positions  to  a  Mercator's  track  chart,  and  calculate,  by 
either  Mercator  or  middle-latitude  sailing,  the  true  course  and  the 
distance  between  each  position. 

This  rule  will  be  sufficiently  correct  for  all  practical  purposes, 
but  if  greater  accuracy  is  desired,  mark  off  the  latitude  for  each 
two  and  a  half  degrees  of  longitude,  instead  of  five  as  before  ex- 
plained. The  student  is  advised  to  procure  a  chart  and  follow  the 
instructions  and  examples  given  thereon,  especially  the  rule  given 
to  find  the  track  beyond  the  limit  of  the  chart. 


DIVISION  III. 


LATITUDE  BY  MERIDIAX  ALTITUDE  OF  THE  SUN. 

The  Observation. — A  few  minutes  before  noon  bring  down  the 
sun's  image  to  the  horizon  and  make  the  lower  edge,  or  lower  limb, 
touch  it  very  nicely.  Watch  the  sun  as  it  rises,  and  each  time  a 
space  is  seen  between  the  sun's  lower  limb  and  the  horizon,  make 
them  touch  again  by  means  of  the  tangent-screw. 

As  the  sun  approaches  the  meridian  it  moves  in  altitude  very 
slowly;  so,  watch  it  closely  until  the  lower  limb  is  seen  to  overlap 
the  horizon,  but  do  not  bring  it  up  again,  because  the  last  altitude 
observed  will  be  the  Meridian  Altitude.  Read  what  is  on  the  sex- 
tant, and  proceed  to  work  the  problem  according  to  the  following 
rules : 

Mark  down  the  day  of  the  month  on  the  left-hand  side  and  the 
longitude  of  the  ship  on  the  right-hand  side  of  the  page.  Convert 
this  longitude  into  time  by  multiplying  by  4  and  dividing  by  60,  or 
use  Table  7.  Place  this  time  under  the  ship's  date,  and  subtract 
it  from  the  ship's  date  if  ship  is  in  East  long,  and  add  if  in  West 
long.     This  will  give  the  Greenwich  Apparent  Time  (G.A.T.). 

To  Correct  the  Declination  for  the  G.A.T. — Take  out  of  the 
Nautical  Almanac,  for  apparent  noon,  the  sun's  declination  and 
its  difference  for  one  hour,  abreast  of  the  Greenwich  date.  Mul- 
tiply the  difference  for  one  hour  by  the  hours  and  tenths  of  hours 
of  the  G.A.T.,  crossing  off  from  the  product  as  many  figures  as 
you  have  decimals  in  the  question.  The  remainder  will  be  sec- 
onds, which  must  be  converted  into  minutes  and  seconds  by  dividing 
by  60,  if  the  remainder  should  be  more  than  60.  The  result  will 
be  the  correction  for  the  declination,  to  be  added  to  the  declination 
if  declination  is  increasing,  but  subtracted  if  declination  is  decreas- 
ing. 

To  Correct  the  Altitude. — Mark  down  the  observed  altitude,  and 
place,  at  some  distance  to  the  right  of  it,  the  sign  of  +  and  of  — . 
Place  the  index  error  (I.E.)  under  the  -f"  or  —  sign,  as  the  case 
may  be.  Then  turn  up  Table  l-l,  and  with  the  height  of  the  eye 
in  feet  above  the  level  of  the  sea  take  out  the  dip  and  place  it  always 


60  Taylor's  Modern  Navigation. 


under  the  —  sign.  Xext  enter  Table  20  with  the  degrees  of  alti- 
tude in  the  altitude  column  and  take  out  the  Refraction  and  place 
it  always  under  the  —  sign.  Then  enter  Table  16  with  the  de- 
grees of  altitude  and  take  out  the  Parallax,  and  place  this  always 
under  the  -\-  sign.  Now  enter  the  Nautical  Almanac  on  page  1, 
and  take  the  sun's  semidiameter  from  abreast  of  the  Greenwich 
date.  Place  this  under  the  +  sign  if  the  lower  limb  (L.L.)  of 
the  sun  is  observed,  and  under  the  —  sign  if  the  upper  limb  (U.L.) 
of  the  sun  is  observed.  Take  the  sum  of  the  -\-  column  and 
the  sum  of  the  —  column  and  subtract  the  lesser  from  the  greater. 
This  will  give  the  correction  for  the  altitude,  to  be  added  to  the 
altitude  if  the  -|-  column  be  the  greater,  and  subtracted  if  the  — 
column  be  the  greater.  The  result  will  be  the  True  Altitude  of 
the  Sun.  Subtract  this  True  Altitude  from  90°,  and  the  remainder 
will  be  the  sun's  Zenith  Distance  (Z.D.),  to  be  named  opposite  to 
the  sun's  bearing.  Now  apply  the  corrected  declination  to  this 
Z.D.,  adding  if  of  the  same  name,  but  subtracting  if  of  contrary 
names.  The  result  will  be  the  Latitude,  which  must  be  named  the 
same  name  as  the  greater. 

If  the  True  Altitude  be  greater  than  90°,  subtract  90°  from  it. 
The  remainder  will  be  the  Z.D.,  to  be  named  the  same  as  the  bear- 


To  Find  the  TeutJts  of  Hours. — The  number  of  times  that  6  will 
go  into  the  minutes  will  give  the  tenths  of  hours. 

The  method  given  in  these  rules  to  correct  the  declination  is  the 
best  for  a  beginner,  but  there  is  another  method  very  much  in  use 
among  experienced  navigators,  namely,  that  of  correcting  the 
declination  for  the  longitude  in  time,  or  from  the  nearest  noon. 
If  the  student  wish  to  correct  his  declination  for  the  longitude  in 
time,  he  must  work  in  the  following  manner:  Convert  the  longi- 
tude into  time,  as  usual,  and  take  out  the  declination  for  the  ship's 
date,  and  multiply  the  difference  in  one  hour  by  the  hours  and 
tenths  of  hours  of  the  longitude  in  time.  This  will  give  the  cor- 
rection for  the  declination,  and  when  applying  this  correction  go 
by  the  following  rules :  If  in  East  longitude,  and  the  declination 
is  increasing,  subtract  the  correction;  but  if  the  declination  is  de- 
creasing, add  the  correction.  If  in  West  longitude,  and  the  declina- 
tion is  decreasing,  subtract  the  correction,  and  if  increasing,  add 
the  correction. 

This  method  of  correcting  the  declination  must  be  used  only  in 
the  problem  of  latitude  by  sun's  Meridian  Altitude. 


Meridian  Altitude.  61 


To  Find  ike  Greenwich  Apparent  Time  {G.A.T.). 
Convert  the  longitude  into  time  by  the  preceding  rule,  and  if  in 
East  longitude,  subtract  from  tlie  ship's  date;  but  if  in  West  longi- 
tude, add  to  ship's  date. 

Example.— 189^,  May  21st,  in  longitude  145°  10'  E.  Required 
the  G.A.T. 

Mark  down  May  21^    0"    0"'    0^  Long.   145°  10'  E. 

Sub.,  because  E.  long.,         9    40  ^  4 

G.A.T.  20^  14'^  19"^  20«  60)580     4Q_ 

Long,  in  time,  9^^  40^"  40« 

In  this  example  we  subtract,  because  the  longitude  is  East;  so 
we  must  say,  40^  from  60^  leaves  20^ ;  then,  as  we  have  borrowed  1 
minute,  we  must  take  40°^  from  59°^,  which  leaves  19™;  then  take 
9^  from  23^  and  we  get  14^,  and  as  we  have  borrowed  1  day,  the 
date  will  now  be  the  20th. 

Example.— 1S94:,  June  1st,  in  long.  92°  17'  E.  Required  the 
G.A.T. 

Mark  down        June  1''    0^^    0"^    O''  Long.   92°  17'  E. 

-     6      9      8  E.  4 

G.A.T.  May  31''  17'^  50"^  52«  60)369    08 

Long,  in  time,  6*^  9"^  08' 

^ote.—Jn  this  case  we  have  to  borrow  a  day. 

Example.— 1S94:,  August  27th,  in  long.  115°  27'  W.  Required 
the  G.A.T. 

Mark  down  Aug.  27^10"    0'»    0«  Long.  115°  27' W. 

Add,  because  W.  long.        7    41    48  4 

G.A.T.  Aug.  27ni^ll^48«  60)461    48 

Long,  in  time,  7^  41"^  48» 

Note.— In  West  longitude  wo  always  add. 


63  Taylor's  Modern  Xavigation. 


To    Correct   the   Swi's   Declination   for   the    G.A.T. 

Example.— ISdi,  November  21st,  in  longitude  49°  59'  E.     Re- 
quired the  G.A.T.,  and  thence  the  declination. 


Nov.  21"^    0^    O''^    0^  Long.  49°  59'  E. 

-3    19    56  E.  4 


G.A.T.  20*1  20*^  40'»    4^^  60)199    56 


Long,  in  time,  S'^  19"^  56* 

Now  look  in  the  Nautical  Almanac  for  the  declination,  which  is 
found  abreast  of  November  20th,  and  when  found,  mark  it  down, 
also  take  out  the  diff.  in  1  hour,  found  abreast  of  the  declination. 
Multiply  this  diff.  in  1  hour  by  the  hours  and  tenths  of  hours  of 
the  G.A.T. 


Decl.  for  Nov.  20=19°  46'  04"  S.  Diff.  in  1  hour,  33".80 

Decl.  increasing,         +1136  20.6 

Correct  decl.  19°  57'  40"  S.  20280 

67600 

60)696.280 

11' 36" 


As  6  minutes  are  one  tenth  of  an  hour,  and  6  goes  into  40  6 
times,  6  must  be  the  tenths  of  hours. 

Note. — Cross  off  as  many  figures  from  the  product  as  there  are 
decimals  in  the  question. 

696  divided  by  60  gives  11'  36",  the  correction  for  the  declina- 
tion. 


Example.— 1894,  March  20th.  in  longitude  179°  10'  W. 

March  20'^   0'^    0'"    0«  Long.  179°  10'  \V. 

+  11    56    40  4 

G.A.T.  20*^  IP  56'"40«  60)716    40 

Long,  in  time,  11''  56'"  40« 


Meridian  Altitude.  63 


Decl.  March  20th,    0°    2'  50"  S.  Diff.  1  hour,  59".22 

Decl.  decreasing,         —11  44  11.9 

Cor.  decl.  0°1)8'  54"  N.  53298 

5922 
5922 


60)704.718 
11' 44" 

Note. — In  this  case  the  sun  is  about  to  cross  the  Equator;  so, 
subtract  the  declination  from  the  correction,  and  the  remainder  is 
the  corrected  declination,  of  an  opposite  name. 

Examples  Complete. 
1894,  February  28th,  in  longitude  120°  W.     Observed  meridian 
altitude  of  sun's  lower  limb,  29°  32'  15",  bearing  South.     Index 
error,  —4'  11".     Height  of  eye,  30  feet.     Find  the  latitude. 


Feb.  28*1 00^^  00°^  00« 
+  8    00    00 


G.A.T.  Feb.  28''    8^  00""  00« 


Decl.         7°  51'  12"  S. 

-7  34 


Cor.  decl.  7°  43'  38"  S. 


Obs.  alt.      29°  32'  15"  S. 

+  5  03 


29 

37 

18 

90 

00 

00 

60 

22 

42 

N. 

7 

43 

38 

S. 

T.  alt. 


Z.D.  60    22  42  N.  +  5' 03" 

Cor.  decl. 

Lat.  52°  39' 04"  N. 


Long.  120°  W. 
4 

60)480 

gh  Qm 

Diff.  J 

Eor  1  hour,  56".78 
8. 

60)454.24 

7'  34" 

+ 
S.D.  16' 11" 
Parlx.  +  08 

+  16  19 
-11  16 

LE.  4' 11' 
Dip,  5  22 
Ref.  1  43 

-11'  16' 

The  longitude  in  time  is  8  hours  West,  and  is  added  to  the  ship's 
date  to  obtain  the  G.A.T.  In  correcting  the  declination  it  will 
be  noticed  that  there  are  only  two  decimal  figures  used,  therefore 


fil 


Taylor's  Modern  Navigation. 


only  two  are  crossed  olf  from  the  product.     The  correction  for  the 
declination  is  subtracted,  because  declination  is  decreasing. 

It  will  also  be  noticed  that  the  Z.D.  and  declination  are  of  con- 
trary names,  and  therefore  one  is  subtracted  from  the  other  to  ob- 
tain the  latitude,  and  the  latitude  is  named  North,  or  same  name 
as  the  greater. 

NERiDiAN  Altitude 
Example  No.  1 


Let  N  Z  S  n  represent  the  plane  of  the  celestial  sphere. 

Z  Zenith,  N  S  Horizon,  n  Nadir,  P  P  Poles,  Q  Q  Equator,  X  Sun, 
obs.  Observer. 

The  student  must  imagine  himself  standing  in  the  center  of  the 
sphere,  at  the  point  marked  obs.,  the  upper  part  of  the  circle  being 
light  and  the  lower  part  darkness. 

Eequired  to  find  the  arc  P  N,  namely,  the  elevation  of  the  Pole. 
which  is  always  equal  to  the  arc  Z  i}.  Either  one  being  equal  to  the 
latitude. 

X  S  Sun's  Altitude. 

Q  X  Declination. 

X  Z  Zenith  distance. 


Meridian  Altitude.  65 


Therefore,  X  S  subtracted  from  90°  (which  is  the  arc  Z  S), 
gives  the  Zenith  distance  X  Z,  so  X  Q  subtracted  from  X  Z  gives 
the  arc  Q  Z,  which  is  the  angle  between  the  celestial  equator  and 
the  zenith,  and  is  equal  to  the  latitude,  or,  in  other  words,  equal  to 
the  elevation  of  P  above  X.  The  name  of  the  latitude  in  this  case 
is  Xnrth,  because  the  Pole  is  elevated  above  the  Xorth  Horizon. 

1894,  September  23d,  in  long.  179°  50'  E.  Obs.  mer.  alt.  of 
Sim's  U.L.  72°  45',  bearing  S.  I.E.  +20'  10".  Height  of  eye, 
21  feet.     Find  the  latitude. 


Sept.  23^' 00'^  00"^  00^  Long.  179°  50'  E. 

-11    59     20  4 


G.A.T.  Sept.  22"  12*^  00°^  40«  60)719  20 

IV  59™20« 


Decl.  0°  13'  15"  N.  Diff.  1  hour,  58".46 

-11  41  12. 


Cor.  decl.  0° 

1'34" 

S. 

N. 

N. 

I.E. 
Pari 

20' 

X. 

+ 
10" 
3 

11692 
5846 

Obs.  alt.  72°  45'  00" 
-33 

60)701.52 

TimT" 

Dip, 
Kef. 

T.  alt.   72  44  27 
90  00  00 

+  20' 

13" 

S.D. 

Z.D.     17  15  33 

+ 

20 

46 

20 

13 

Cor.  decl.    0     1   34    N.  -00' 33' 

Lat.  17^17' 07"  N. 


The  longitude  in  time  is  subtracted  from  ship's  date  to  obtain 
G.A.T.,  because  longitude  is  East.  In  this  case  the  upper  limb 
being  observed,  the  semidiameter  is  placed  in  the  —  column. 

Taylor's  Mod.  Nav.   5. 


t)6 


Taylor's  Modern  Navigation. 


Examples  for  Fracticc. 
1894,  December  21st,  in  long.  53°  40'  E.     Obs.  mer.  alt.  of  sun's 
I..L.  89°  58'  00",  bearing  S.       I.E.  +2'  00".     Height  of  eye,  20 
feet.     Find  the  latitude. 


Dec.  'il'i  00"  00'"  00« 
3    34     40 


Long.  53°  40'  E. 
4 


G.A.T.  Dec.  20"^  20"  25" 
24    00 

3"  35" 


20' 


60)214  40 
Long,  in  time,  3"  34"'  40" 
(time  from  nearest  noon). 

Here  it  will  be  noticed  that  the  hours  being  20,  it  is  more  correct 
to  work  from  the  nearest  noon,  namely,  the  21st,  when  taking  out 
the  sun's  declination;  so,  subtract  the  hours  and  minutes  from  24 
and  use  the  result  to  correct  the  declination ;  but  as  we  are  working 
backward,  note  if  the  declination  is  increasing  or  decreasing,  read- 
ing backwards  from  the  21st. 


Decl.         23°  27'  18' 
-   1 

Cor.  decl.  23°  27M7" 


G  (It  IS  reaUy  17". 6,  but  we 
call  it  18",  because  the 
decimal  is  more  than  5.) 


0.40  hourly  diff 
3.6    nearly. 

240 
120 

1".440  correction. 


Obs.  mer.  alt.  L.L.  89°  58'  00"  S.         I.E.      2'  00' 


T.  alt. 

Z.D. 
Cor.  decl. 

Lat. 


+  13  55 

90    11  55 
90    00  00 

00    11  55 
23    27  17 


23°  39'  12"  S. 


S.D.   16  18 
Parlx.      00 

+  18  18 
-  4  23 

+  13"'^' 


Dip, 
Ref. 


4' 23' 
0  00 

4'  23' 


In  this  case  the  true  altitude  is  greater  than  90°  ;  so,  subtract 
90°  from  the  true  altitude,  and  keep  the  name  of  the  bearing  for 
the  Z.D. 


Caution  to  the  Rising  Generation  of  Navigators. 

We  address  these  remark,-;  especially  to  young  men.       Lecky,  in 
his    valuable    book    entitled     Wrlid-Irs    in     I'mclical    Navigation, 


Meridian  Altitude.  67 


directs  the  attention  of  seamen  to  the  hizy  and  criminal  habit 
of  some  old  and  so-called  experienced  navigators,  whereby  they  find 
the  latitude  by  subtracting  the  sun's  altitude  from  the  constant, 
89°  48'.  It  is  ivrong,  very  wrong,  and  the  master  or  officer  doing 
so  lazy  a  thing  is  not  fit  to  hold  his  position.  Some  of  them  say, 
"I  know  it  is  not  right,  but  it  comes  out  near  enough." 

Young  men,  do  not  allow  any  old  Sindbad  or  Billie  Ringbolt  to 
advise  you  that  it  is  near  enough,  for  the  following  reasons :  1.  The 
correction  for  height  of  eye  is  governed  by  the  number  of  feet 
that  the  observer  is  elevated  above  the  sea-level,  but  the  lazy  man 
with  his  lazy  method  does  not  take  this  into  consideration,  but 
uses  the  same  correction,  no  matter  if  he  is  standing  on  the  top 
of  his  deck-load,  on  the  deck  awash,  or  on  the  bridge  of  a  high- 
sided  steamer.  2.  The  refraction  is  governed  by  the  amount  of  the 
sun's  altitude  as  seen  by  inspecting  the  table,  but  the  lazy  man  does 
not  take  even  this  into  consideration,  but  uses  the  same  old  cor- 
rection, no  matter  if  the  sun  is  right  above  his  head  or  only  a  few 
degrees  above  the  horizon.  The  difference  between  the  working 
of  the  correct  and  incorrect  methods  amounts  to  but  few  figures, 
but  it  may  give,  under  certain  conditions,  an  error  amounting  to 
more  than  six  miles,  which,  from  the  lazy  man's  point  of  view, 
m.ay  not  be  considerable,  but  from  a  good  navigator's  point  of  view, 
is  more  than  considerable,  for  the  reason  that  if  the  sight  to  ascer- 
tain the  longitude  is  worked  up  with  this  wrong  latitude  a  very  large 
error  will  be  made  in  the  longitude,  according  to  the  sun's  true 
azimuth  at  time  of  sight.  The  amount  and  condition  will  be  fur- 
ther discussed  under  the  head  of  longitude. 

Special  Table  to  Correct  Altitude. 

At  the  end  of  this  book  will  be  found  a  table  for  the  correction 
of  the  sun's  altitude,  lower  limb,  w-hich  may  be  used  with  ab- 
solute confidence  for  practice  at  sea.  It  is  simply  a  mean  of  the 
corrections  used,  namely,  Semidiameter,  Dip,  Refraction,  and 
Parallax,  with  a  small  correction  to  be  applied  according  to  the 
time  of  year,  and  may  be  entered  in  the  following  manner :  Look 
on  top  of  page  for  the  height  of  eye  above  the  level  of  the  sea  in 
feet,  and  on  the  left-hand  side  for  the  altitude,  then  under  the 
feet  and  abreast  of  the  altitude  will  be  found  the  correction,  to  Uq 
added  to  the  altitude  ahcaijs.  The  correction  is  given  in  minutea, 
and  tenths  of  minutes;  so,  to  convert  the  tenths  into  seconds^ 
simply  multiply  them  by  6.  ^_^^ 


68 


Taylor's  Modern  Navigation. 


Practical  Illustration    of    IJoiv    to     Work   the  Meridian   Altitude 
Problem  at  Sea. — Short  hut  Correct  Method. 


1894,  December  20th,  in  long.  170°  10'  W.  Obs.  mer  alt.  of 
sun's  L.L.  52°  20'  18",  bearing  S.  I.E.  +2'  20".  Height  of  eye, 
26  feet.    Find  the  latitude. 

Dec.  20th,  decl.  at  noon,  23°  2(i'  54"  S. 

Added,  because  decl.  is  increas-  j        _l  1  Q    AH 
ing  and  ship  is  in  W.  long.  <,       -(-  io    UU 


decl. 


23°  27'  12"  S. 


Long.  170°  10'  W. 

By  Table  7. 

170°  =  11^^  20"' 00^ 

10'  =00   00    40 


Long,  in  time,  11^'  20"'  40^ 


Obs.  alt.  L.L.  52°  20'  18"  S. 
Cor. 

T.  alt. 


Z.D. 

Cor.  decl 

Lat. 

Note.- 


+  12 

38 

52 

32 

56 

90 

00  00 

37 

27 

04 

23 

27 

12 

N. 
S. 

13°  59'  52"  N. 


+ 

LE.   2'  20" 

Diff, 

.Ihi 

■.  1".58 

Cor. +  10  18 

11.3 

+  12' 38" 

474 

158 

158 

17.854 

(18' 

'  nearly.) 

This  work  may  be  still  further  abbreviated  in  practice 
by  omitting  the  seconds  and  working  to  the  minutes  of  arc  only. 
Also,  it  is  not  necessary  to  use  the  longitude  in  time,  but  instead, 
simply  read  the  chronometer  hours  and  minutes,  applying,  of  course, 
its  correction  and  using  this  time  to  correct  the  declination,  using 
the  mean  page  of  Almanac  because  the  chronometer  shows  Green- 
wich mean  time. 

Meridian  Altitude. 
No.  1. 

1894,  September  23d,  in  long.  150°  10'  E. ;  obs.  mer.  alt.  of  sun'< 
L.L.  75°  40'  20",  bearing  S. ;  I.E.  +5'  40" ;  eye  14  feet.  Required 
the  latitude. 

Answer.— G.A.T.  22-^  IS'^  59"'  20^;  cor.  decl.  0°  0'  24"  S. ;  T. 
alt.  75°  58'  6";  lat.  14°  1'  30"  X. 

No.  2. 

1894,  February  22d,  in  long.  100°  42'  E. ;  obs.  mer.  alt.  of  sun's 
L.L.  40°  40',  bearing  S. ;  I.E.  +12'  12" ;  eye  24  feet.  Required  the 
latitude. 

Answer.— Cor.  decl.  10°  11'  17"  S. ;  T.  alt.  41°  2'  35";  lat.  38° 
46'  08"  N. 


Meridian  Altitude.  69 


No.  3. 


189-4.  January  IGtli.  in  long.  52°  49'  W. ;  obs.  nier.  alt.  of  sun's 
L.L.  50°  10'  10",  bearing  S.;  I.E.  —5'  40";  eye  30  feet.  Required 
the  latitude. 

Answer.— Cor.  decl.  20°  51'  22"  S.;  T.  alt.  50°  14'  42";  lat.  18° 
53'  oG"  X. 

No.  4. 

1894,  March  2nth,  in  long.  170°  50'  E;  obs.  mer.  alt.  of  sun's 
L.L.  60°  20'  10".  bearing  X. ;  I.E.  +2'  10" ;  eye  12  feet.  Required 
the  latitude. 

Answer.— Cor.  decl.  0°  14'  5"  S.;  T.  alt.  60°  34'  31" ;  lat.  29°  39' 
34"  S. 

Xo.  5. 

1894,  August  20th,  in  long.  170°  10'  E.;  obs.  rom-.  alt.  of  sun's 
L.L.  39°  49',  bearing  X. ;  I.E.  —7'  40" ;  eye  26  feet  Required  the 
latitude. 

Answer.— Cor.  decl  12°  32'  04"  X.;  T.  alt.  31°  51  09";  lat.  37° 
36'  47"  S. 


Xo.  6. 


1894,  March  21st,  in  long.  179°  59'  E. ;  obs.  mor.  alt.  of  sun's  L.L. 
89°  50'  40",  bearing  X. ;  I.E.  —10'  16" ;  eye  32  feet.  Required  the 
latitude. 

Answer.- Cor.  decl.  0°  9'  1"  X.;  T.  alt.  89°  50'  54":  lat.  0°  0' 

5"  S. 

Xo.  7. 

1894,  March  17th,  in  long.  92°  40'  E.;  obs.  mer.  alt.  of  sun's 
L.L.  89°  54'  10",  bearing  S. ;  I.E.  +2'  10" ;  eye  22  feet.  Required 
the  latitude. 

Answer.— Cor.  decl.  1°  20'  2"  S.;  T.  alt.  90°  7'  50";  lat.  1°  27' 
52"  S. 


70  Taylor's  Modern  Navigation. 

No.  8. 

1894,  August  12th,  in  long.  45°  40'  W.;  obs.  mer.  alt.  of  sun's 
L.L.  48°  50'  10",  bearing  S.;  I.E.  +5'  10";  eye  18  feet.  Required 
the  latitude. 

Answer.— Cor.  decl.  14°  52'  26"  N.;  T.  alt.  49°  6'  16";  lat.  55° 
46'  10"  N. 


No.  9. 


1894,  September  22d,  in  long.  101°  42'  W. ;  obs.  mer.  alt.  of  sun's 
L.L.  47°  21'  00",  bearing  S. ;  I.E.  +4'  10" ;  eye  30  feet.  Required 
the  latitude. 

Answer.— Cor.  decl.  0°  6'  38"  N.;  T.  alt.  47°  34'  59";  lat.  42° 
31'  39"  N. 

No.  10. 

1894,  October  1st,  in  long.  68°  14'  E. ;  obs.  mer.  alt.  of  sun's  L.L. 
49°  15'  10",  bearing  S.;  I.E.  —5'  40";  eye  18  feet.  Required  the 
latitude. 

Answer.— Cor.  decl.  3°  12'  52"  S.;  T.  alt.  49°  20'  37";  lat.  37° 
26'  31"  N. 

No.  11. 

1894,  January  15th,  in  long.  97°  15'  W.;  obs.  mer.  alt.  of  sun's 
L.L.  54°  20'  30",  bearing  N. ;  I.E.  +15'  20" ;  eye  10  feet.  Required 
the  latitude. 

Answer.— Cor.  decl.  21°  1'  25"  S. ;  T.  alt.  54°  48'  26";  lat.  56° 
12'  59"  S. 

No.  12. 

1894,  July  1st,  in  long.  98°  10'  E. ;  obs.  mer.  alt.  of  sun's  U.L. 
89°  59'  40",  bearing  S.;  I.E.  +2'  10";  eye  18  feet.  Required  the 
latitude. 

Answer.— Cor.  decl.  23°  7'  40"  N.;  T.  alt.  89°  41'  55";  lat.  23° 
25'  45"  N. 


Meridian  Altitude.  71 


No.  13. 

1894,  May  1st,  in  long.  109°  10'  E.;  obs.  mer.  alt.  of  sun's 
ILL.  48°  SO'  10",  bearing  N. ;  I.E.  +1'  10"  ;  eye  22  feet.  Required 
the  latitude. 

Answer.— Cor.  decl.  15°  8'  57"  N.;  T.  alt.  48°  00'  04";  lat.  26° 
50'  59"  S. 

No.  14. 

1894.  March  21st,  in  long.  104°  15'  E. ;  obs.  mer.  alt.  of  sun's 
U.L.  41°  50'  00",  bearing  N. ;  I.E.  +10'  15"  ;  eye  8  feet.  Required 
the  latitude. 

Answer.— Cor.  decl.  0°  10'  00"  N.;  T.  alt.  41°  40'  26";  lat.  48° 
9'  34"  S. 

Note. — The  examples  for  practice  here  given  are  all  worked  for 
every  second ;  but  if  the  student  use  the  table  for  the  correction  of 
the  altitude,  the  result  will  be  within  one  mile  of  the  above  answers, 
with  the  exception  of  the  upper-limb  sights,  the  table  being  in- 
tended for  lower-limb  sights  only. 

LATITUDE    BY    MERIDIAN    ALTITUDE    OF    THE    SUN 

BELOW  THE  POLE. 

(Midnight  Sun.) 

Very  Useful  for  Seamen  Navigating  in  the  Polar  Regions. 

Rule. 

Mark  down  the  date,  and  to  the  right  of  it  mark  12^^  O""  0%  as 
seen  in  example.  Convert  the  longitude  into  time,  and  apply  it  to 
the  ship's  date,  etc.,  adding  if  ship  is  in  West  longitude  and  sub- 
tracting if  in  East.     The  result  will  be  the  G.A.T. 

Next  enter  the  Nautical  Almanac  and  take  out  the  declination 
from  the  apparent  page,  correcting  it  for  the  G.A.T. 

Correct  the  observed  altitude  for  I.E.,  Dip.,  S.D.,  Ref..  and 
Parlx.,  and  obtain  the  true  altitude. 

Subtract  the  corrected  declination  from  90°.  The  remainder 
will  be  the  Polar  Distance.  To  the  Polar  Distance  (P.D.)  always 
add  the  true  altitude.  The  result  will  be  the  latitude,  which  will 
be  named  the  same  as  the  declination. 

The  sun  is  12  hours  later  coming  to  the  Meridian  helow  the  Pole ; 
so  the  apparent  time  at  place  must  be  12"^  O""  0^     When  the  sun 


Taylor's  Modern  Xavigation. 


is  approaching  the  Meridian  above  the  Pole,  it  moves  from  East  to 
West,  but  when  approaching  the  Meridian  below  the  Pole,  it  moves 
from  West  to  East. 


Example. — 1894,  July  20th,  at  midnight,  the  ship  being  in  long. 
175°  20'  W.;  the  altitude  of  the  sun's  L.L.  below  the  Pole  9°  48' 
00" ;  I.E.  00'  00"  :  lieiglit  of  eye  24  feet.     Find  the  latitude. 


July     20*^  12^^    0'"    O''  Long.  175°  20'  W. 

+  11    41     20  4 


G.A.T.  20  23    41    20  60)701    20 

2^  00  "TlMl^O^ 

00^  19"^  from  July  21st,  at  noon. 


Decl.  21st,     20°  26'  34"  N.  Diff.  1  hour,  29".16 
-  9  _.3_ 

Sub.  always,  20    26  43    N.  8.748 

90    00  00  (9"  -nearly.) 


P.D. 

69°  33'  17" 

Obs.  alt.  L 

.L.  9°  48' 00" 
+  5  44 

N. 

+ 
S.D.   15' 47" 
Parlx.     9 

Dip,  4'  48" 
Ref.  5  24 

True  alt. 
P.D. 

9  53  44 
69  33  17 

+  15  56 
-10  12 

+  ^44" 

-10' 12" 

Lat. 

79°  27' 01" 

The  same  result  will  be  obtained  if,  instead  of  finding  the  polar 
distance  (P.D.),  90°  is  added  to  the  true  altitude  and  the  declina- 
tion subtracted  from  the  sum. 

It  may  not  be  amiss  for  the  student  to  understand  the  following 
short  rule: 

If  the  P.D.  of  a  celestial  body  be  less  than  the  latitude,  it  will 
not  set,  but  will  pass  the  meridian  twice  in  24  hours;  hence  the 
name,  circum polar.  This  should  be  remembered  when  studying 
the  problem  of  latitude  by  a  fixed  star,  in  the  following  section. 


Meridian  Altitude. 


73 


Example  below  the  Pole 

2       P 


Required,  the  arc  P  S. 

N  S  Horizon,  I'  V  Poles,  Q  Q  Equator.  X  Sun,  Z  Zenith,  obs. 
Observer. 

X  S  Sun's  Altitude. 

X  Q  Declination. 

P  to  Q  00° :  therefore,  if  X  Q  i?  subtracted  from  it  the  ]).)lar  dist- 
ance is  found  X  P,  now  if  the  arc  X  P  is  known  and  also  the  Alti- 
tude, or  arc  X  S,  to  obtain  the  arc  P  S,  the  sum  of  X  S  and  X  P 
must  be  taken  to  obtain  the  elevation  of  the  Pole.  This  illustration 
will  give  South  latitude  because  the  Pole  is  elevated  above  the 
South  Horizon. 


74  Taylor's  Modern  Navigation. 


LATITUDE  BY  MERIDIAN  ALTITUDE  OF  A  FIXED  STAR 

It  is  generally  advisable  for  those  who  wish  to  observe  the  stars 
to  supply  themselves  with  a  star-chart,  so  that  they  can  pick  out  at 
sight  the  particular  star  required  at  any  time.  They  should  com- 
mence, when  learning  the  stars,  to  locate  the  principal  constella- 
tions, such  as  the  constellation  of  Orion  or  of  the  Great  Bear,  and 
from  these,  by  striking  lines  and  angles,  to  locate  others.  It  be- 
comes necessary,  before  making  the  observation,  to  know  at  what 
time  the  star  will  pass  the  meridian ;  then,  when  this  is  ascertained, 
the  observer  should  bring  the  star  down  to  the  horizon  by  means 
of  the  sextant,  according  to  the  rule  given  in  the  chapter  relating  to 
the  sextant,  watching  the  star  until  it  arrives  at  its  greatest  altitude 
and  using  this  altitude  to  find  the  latitude  by  the  rule  given  here. 
Observations  of  stars  should  be  taken  during  twilight,  as  far  as 
possible,  as  the  horizon  is  well  defined  at  that  time,  but  if  the  true 
place  of  the  horizon  is  doubtful,  take  one  observation  from  the  North 
and  one  from  the  South,  and  the  mean  of  the  two  will  bo  the  lati- 
tude, very  nearly. 

Rule  to  Find  the  Time  of  Meridian  Passage  of  a  Fixed  Star. 

From  the  Nautical  Almanac,  and  for  the  nearest  day,  take  out 
the  star's  Right  Ascension,  under  the  heading  of  fixed  stars. 

From  the  Nautical  Almanac,  page  2  of  the  month,  take  out  the 
Sidereal  Time,  which  is  the  Right  Ascension  of  the  mean  sun. 
Then  subtract  the  Sidereal  Time  from  the  star's  Right  Ascension,, 
borrowing  24  hours  if  necessary.  The  remainder  will  be  the  ap- 
proximate mean  time  of  the  star's  passing  the  meridian.  This  will 
give  the  mean  time  of  the  Star's  Meridian  Passage,  sufficiently  near 
for  the  ordinary  practice  of  navigation.  If  the  apparent  time  is 
required,  apply  the  equation  as  given  on  page  2  of  the  numth. 

Example.— J -a^nuKTy  1,  1894,  the  time  of  the  Meridian  Passage 
of  the  star  a  Piscis  Australis  (Fomalhavt)  was  required. 

Jan.  1st,  right  ascension  of  star,  22''  51'"  4^" 

Sid.  time,  or  right  ascension  of  mean  sun,  18    44     25)   (subtract.) 

4      7     19  M.T.S. 
Equation  of  time,  —3     53 

App.  time  of  star  passing  meridian,  4''    3"^  26«  A.T.S.,  p.m. 

If  the  result  is  greater  than  12  hours,  reject  12.  The  remainder 
will  be  the  time  in  the  morning. 


Meridian  Altitudb.  75 


Rule  to  Find  What  Star  is  Approaching  the  Meridian. 

In  quite  a  number  of  epitouios  a  table  is  given  for  A.T.S.  of  star's 
passiug  the  meridian,  but  if  not  given,  the  following  is  a  good  rule 
to  tell  what  star  is  near  the  meridian. 

Add  the  Sidereal  Time  to  the  Astronomical  M.T.S.,  rejecting  24 
hours  if  necessary.  The  result  will  be  the  approximate  Right 
Ascension  of  the  Meridian  (R.A.  of  Mer.). 

Turn  to  table  of  Fixed  Stars  in  Nautical  Almanac  and  look  for 
this  approximate  R.A.  of  Mer.,  and  when  found,  take  the  name  of 
the  star  abreast.  The  difference  between  the  star  with  less  R.A.  and 
the  R.A.  of  Mer.  will  give  the  star  West  and  falling,  and  the  differ- 
ence between  the  star  with  greater  R.A.  and  the  R.A.  of  Mer.  will 
give  the  star  East  and  rising,  which  will  be  the  star  to  observe  for 
latitude. 

If  the  decl.  mid  lat.  are  same  name — 

In  North  lat.  the  star  will  bear  Xorth  if  decl.  is  greater  than  lat. 
and  South  if  less. 

In  South  lat.  the  star  will  bear  South  if  decl.  is  greater  than  lat. 
and  North  if  less. 

If  lat.  and  decl.  are  contrary  names,  the  star  will  bear  North  if 
decl.  is  North,  and  South  if  decl.  is  South. 

Declination  is  Celestial  Latitude. 

Stars  whose  declinations  are  greater  than  the  colat.  when  lat. 
and  decl.  are  different  names,  will  not  rise  above  the  horizon. 

RULE  TO  COMPUTE  THE  MERIDIAN  ALTITUDE  OF  A 
FIXED  STAR. 

It  frequently  occurs  at  sea  that  star-charts  are  not  available,  or 
that  the  observer  has  very  little  knowledge  in  regard  to  the  posi- 
tion of  the  different  stars.  In  such  a  case  proceed  as  follows :  Find 
the  latitude  of  the  ship,  by  dead-reckoning,  as  accurately  as  pos- 
sible, and  subtract  it  from  90°.    The  result  will  be  the  colatitude. 

To  the  colatitude,  retaining  the  name  of  the  latitude  itself,  ap- 
ply the  star's  declination,  adding  when  of  same  name  and  subtract- 
ing when  contrary  names.  The  result  will  be  the  approximate 
meridian  altitude,  to  be  reckoned  from  the  southern  horizon  when 
latitude  is  North,  and  from  the  northern  when  latitude  is  South; 
"but  when  the  sum  is  greater  than  90°,  subtract  it  from  180°,  and 
nckon  from  the  North  in  North  latitude  and  from  the  South  in 
j5outh  latitude. 


T.ii'LOR's    ]\10DERX    XaVIGATIOX. 


Xow  jjlace  the  altitude  on  the  sextant  and  direct  your  sight  to 
the  northern  or  southern  horizon,  according  to  the  name  of  the  al- 
titude. Then  on  or  near  the  horizon  the  star  will  be  seen.  Make 
it  touch  the  horizon  nicely  by  means  of  the  tangent-screw,  watch- 
ing it  until  it  has  obtained  its  greatest  altitude.  This  will  give 
you  the  meridian  altitude  of  the  star  required. 

Example. — Find  the  approx.  raer.  alt.  of  star  Sirius,  lat.  of  ship 
by  dead-reckoning  40°  20'  S. 

Lat.     40°  20'  S. 
90    00 


Colat.  49    40  S. 
Decl.   16    34  S. 


Approx.  alt.  bearing  N.  66°  14' 

Rule  lo  Find  the  Latitude. — Mark  down  the  altitude,  and  to  the 
right  of  it  place  down  the  +  and  —  signs.  Mark  down  the  I.E., 
if  any,  under  the  sign  corresponding  to  its  name.  Take  out  the  dip 
for  the  number  of  feet  and  place  it  under  the  —  sign.  Next  take 
out  the  refraction  for  the  altitude,  and  mark  it  down  under  the  — 
sign  also.  By  taking  the  sum  of  each  column  and  subtracting  the 
lesser  from  the  greater,  will  be  obtained  the  correction  for  the  al- 
titude, to  be  subtracted  from  the  altitude  if  the  —  sign  is  the 
greater,  and  added  if  the  -f  sign  is  the  greater,  the  same  as  when 
working  meridian  altitude  of  tlie  sun.  (S.D.  and  Parlx.  are  not 
required  in  this  problem.)  This  will  give  the  true  altitude  of  the 
star,  to  be  subtracted  from  90°  to  get  the  Z.D.,  which  is  to  be 
named  opposite  to  tlie  bearing  of  the  star.  Now  enter  the  Nautical 
Almanac  with  the  name  of  the  star,  and  take  therefrom  the  star's 
declination,  which  may  be  used  as  it  stands,  because  the  declination 
of  a  star,  as  may  be  seen  by  reference  to  the  column  of  annual 
variation,  changes  but  very  little  in  a  whole  year.  A  —  sign  is 
invfixed  when  the  declination  is  South,  and  a  -f  sign  is  prefixed 
wlien  the  declination  is  North.  Apply  this  declination  to  the  Z.D.. 
adding  if  same  name,  and  subtracting  if  contrary  names.  The 
result  will  be  the  latitude,  to  be  named  the  same  as  the  greater. 

iiVr///////r'.— October  20,  1894,  mer.  alt.  of  star  a  Piscis  Australis 
{Fomalhaut)  was  30°  10'  IG",  bearing  South.  F.E.  00'  00".  Hei^rht 
of  eye  18fe<'t.  ° 


Meridian'  Altitude.  77 


Obs.  alt. 

30°  10'  16"  S. 

Dip,  4'  09" 

-  5  50 

Ref.  1  41 

T.  alt. 

80  04  26 
90  00  00 

-5' 50" 

Z.D. 

59  55  34  N. 

Decl. 

30  11  2  S. 

Lat. 

29°  44'  32"  N. 

Examples  fur  Practice. 

1894,  Feb.  3d.  obs.  mor.  alt.  of  .itar  «  Bootis   {Arctwus)   80° 
22'  00",  bearing  S. ;  I.E.  +2'  10";  eye  16  ft.     Find  the  latitude. 
Answer.— Latitude  29°  23'  59"  N. 

1894,  March  8th,  obs.  mer.  alt.  of  star  a  Virginis   (Spka)   61° 
30'  00",  bearing  ^.;  I.E.  —6'  30";  eye  21  ft.   Find  the  latitude. 
Answer.— Latitude  39°  18'  00"  S. 

1894,  April  20th,  obs.  mer.  alt.  of  star  a  Crucis  9°  34'  00",  bear- 
ing S. ;  I.E.  +12'  50"  ;  eye  18  ft.    Find  the  latitude. 
Answer.— Latitude  7°  52'  12"  X. 

1894,  May  15th,  obs.  mer.  alt.  of  star  «  Canis  Majoris  {Sirius) 
43°  51'  00",  bearing  X. ;  I.E.  0'  00" ;  eye  10  ft.     Find  the  latitude. 
Answer.— Latitude  62°  47'  22°  S. 

1894,  Dec.  16th,  obs.  mer.  alt.  of  star  a  Canis  Minoris 
{Procyon)  50°  16'  40",  bearing  X.;  i.K.  00'  00";  eye  12  ft.  Find 
the  latitude. 

Answer.— Latitude  34°  17'  46"  S. 

1894,  July  31st,  obs.  mer.  alt.  of  star  /?  Scorpii  30°  40'  16", 
bearing  S. ;  I.E.  —2'  30"  ;  eye  8  ft.    Find  the  latitude. 
Answer.— Latitude  39°  55'  44"  N. 


LATITUDE  BY  MEEIDIAX  ALTITUDE  OF  A  PLAXET. 

The  observation  is  made  similarly  to  that  of  a  star,  by  either 
bringing  the  planet's  image  down  to  the  horizon  by  means  of  sex- 
tant or  by  computing  the  altitude  and  setting  the  sextant  thereto 
as  already  explained  in  the  preceding  chapter  on  stars. 

When  correcting  the  altitude  the  same  method  may  be  used  as 
for  a  star.    Although  there  is  a  sensible  semidiameter  to  the  planets 


TAiLOR's  Modern  Xavigation. 


Yenus  and  Jupiter,  \vith  Mars  aud  Saturn  it  is  very  small. 
For  sea  practice,  however,  both  S.D,  and  parallax  may  be  entirely 
ignored. 

It  is  generally  supposed  among  seamen  that  planets  can  be  ob- 
served at  night  only.  This  is  not  so  in  the  case  of  Venus,  for  a 
very  good  result  may  be  obtained  from  this  planet,  sometimes,  dur- 
ing the  morning  hours. 

Thus,  suppose  that  by  reference  to  the  Nautical  Almanac,  under 
the  planet's  name,  and  abreast  of  the  date,  the  time  of  its  meridian 
passage  should  be  found  to  be  lO*'  a.m.  Then  with  the  lat.  by 
dead-reckoning  and  its  decl.  compute  the  approximate  mer.  alt. 
Set  this  mer.  alt.  on  the  sextant  and  direct  the  sight  to  either  the 
North  or  South  points  off  the  horizon,  and  on  or  near  it  will  be 
seen  the  planet's  image.  Watch  it  as  it  rises  and  note  the  greatest 
altitude,  and  proceed  to  work  the  problem. 

To  be  a  successful  observer  it  is  very  necessary  that  a  good  sex- 
tant be  used,  with  the  silvering  in  excellent  condition.  It  should 
also  be  fitted  with  a  good  star-finder  or  star-telescope. 

When  making  the  contact  with  a  star  or  planet  and  the  horizon, 
endeavor  to  measure  from  its  center,  especially  if  it  is  the  intention 
to  ignore  the  S.D. 

If  the  planet's  parallax  in  altitude  is  used,  reference  must  be 
made  to  Table  17  of  Bowditch,  but,  as  a  rule,  it  is  so  small  that  no 
attention  need  be  given  it. 

The  student,  after  reading  the  foregoing,  will  no  doubt  discern 
that  a  knowledge  of  the  time  of  the  planet's  passage  ■  over  the 
meridian  will  be  very  essential,  so  that  he  may  know  about  what 
time  to  observe.  This  will  be  found  by  simply  referring  to  the 
Almanac,  under  the  heading  of  meridian  passage,  and  may  be  taken 
out  at  sight  for  ordinary  practice,  but  if  greater  accuracy  is  de- 
sired, correct  it  for  the  longitude  of  the  ship. 

To  Correct  the  Planet's  Declination. 

Mark  down  the  astronomical  date  and  time  of  meridian  passage 
and  apply  the  longitude  in  time,  adding  if  West  and  subtracting  if 
East.  The  result  will  be  the  M.T.G.,  corresponding  to  the  merid- 
ian passage  at  ship. 

With  this  mean  time  at  Greenwich  enter  the  Nautical  Almanac 
and  take  out  the  decl.  and  multiply  the  var.  of  decl.  in  one  hour 
by  the  hours  and  tenths  of  hours,  and  obtain  the  correction.  Add 
to  or  subtract  from  this  correction  the  decl.  according  as  it  is  in- 
creasing or  decreasing.    The  result  will  be  the  cor.  decl. 


Meridian  Altitude.  79 


To  CoiujEcT  THE  Altitude. 

Apply  the  I.E.,  if  any,  also  the  clip  and  ref.  same  as  for  star  al- 
titude, and  find  the  true  altitude  of  the  planet. 

Subtract  the  true  altitude  from  90°  and  obtain  the  Z.D.,  and 
name  it  opposite  to  the  bearing. 

To  FixD  the  Latitude. 

If  the  Z.D.  and  decl.  have  same  name,  add  them  together,  but 
if  contrary  names,  subtract.  The  result  will  be  the  latitude,  to  be 
named  always  the  same  as  the  greater. 

Example. — 1894,  Xovember  ITth,  a.m.  at  ship,  in  long.  43°  20' 
E.;  the  obs.  mer.  alt.  of  planet  Jupiter  (center)  was  Vi°  Id'  10", 
Ix'aring  North ;  height  of  eye  12  feet.    Find  the  latitude. 

Nov.  16^'  14'>  39'"  00-^  mer.  pass. 
-  2    53    20 


WW  45"'  40^  M.T.( 


Decl.  23°  2'  36"  N. 

+  08 

Cor.  decl.  23°  2'  42"  N. 


Central  alt. 

27°  10'  10" 
-  5   17 

X. 

T.  alt. 

27      4  53 
90    00  00 

Z.D. 

62    55     7 

s. 

Decl. 

23      2  42 

N. 

Lat. 

39°  52'  25" 

'  S. 

Long.  43° 

20' 

4 

E. 

60)173 

20 

211 

53"^ 

'20^ 

0".69 

11.7 

483 

069 

069 

08.073 

Dip,  3' 

24" 

Ref.  1 

53 

5'  1- 


Examples  for  Practice. 
1894,  March  31st,  a.m.  at  ship,  in  long.  112°  17'  E.;  obs.  mer. 
alt.  of  planet  Mars  (center)   60°  2?'  10",  bearing  North;  height 
of  eye  18  feet.    Find  the  latitude. 


80 


Taylor's  Modern  Navigation. 


It  is  always  necessary  to  work  with  astronomical  time;  so,  as  it 
is  A.M.  at  place,  the  meridian  passage  and  date  must  be  taken  from 
the  day  before;  namely,  the  30th. 


March  30^  19'^  43'"  30^  mer.  pass. 

-  7    29    08   long,  in  time. 

Loi 

ig.  112° 

17'  E. 

4 

30d  12^^  14""  22«  M.T.G. 

60)449 

08 

Planet's  decl.  March  30th =20°  49'    9" 
-  4  13 

7h 
6C 

29'"  08« 

20'.77 
12.2 

Cor.  decl.                                 20°  44'  56" 

4154 
4154 
2077 

1)253.394 

4'  13" 


Central  alt.  60°  27'  10"  N. 
-  4  43 


T.  alt. 

60 

22  27 

90 

00  00 

Z.D. 

29 

37  33 

S. 

Decl. 

20 

44  56 

S. 

Lat. 


50°  22'  29"  S. 


Dip,  4'  09" 
Ref.      34 

-4'  43" 


1894,  January  26th,  p.m.  at  ship,  in  long.  30°  23'  W. ;  obs.  mer. 
alt.  of  the  planet  Venus  (center)  47°  10'  20".  bearing  South; 
height  of  eye  35  feet.     Find  the  latitude. 


Jan.  26''  2'^  00"'  00^  mer.  pass. 
+  2      1     32 


M.T.G.  26M»'    l'"32« 


Decl 

5° 

7'  14" 
-2  11 

'  S. 

Cor. 

decl. 

5° 

5'  03" 

■s. 

Long.  30°  23'  W 

4 

60)121  32 

2h  pn  328 

32".83 

4 

60^13732 

2'  11' 


Meridian  Altitude.  81 


Central 

alt.  47°  10'  20" 
-  6  42 

■s. 

T.  alt. 

47   3  38 
90  00  00 

Z.D. 

42  56  22 

N. 

Decl. 

5   5  3 

S. 

Lat. 

37°  51' 19" 

N. 

Dip,  5'  48' 
Ref.       54 


-6'  42' 


LATITUDE  BY  OBSERVED  ALTITUDE  OF  THE  POLE- 
STAR  WHEN  OUT  OF  THE  MERIDIAN. 

The  Pole-star  is  not  situated  exactly  at  the  pole,  but  is  revolving 
around  it  at  a  distance  of  about  lyi  °.  It  is  the  nearest  circum- 
polar  star,  and  in  the  United  States  never  sets. 

If  the  Pole-star  were  situated  exactly  at  the  pole,  its  altitude 
would  always  be  equal  "to  the  observer's  latitude.  For  example,  if 
the  observer  were  on  the  Equator,  the  Pole-star  would  be  on  the 
horizon,  but  if  he  advanced  10°  to  the  North,  the  Pole-star  would 
be  10°  above  the  horizon  and  the  observer  in  10°  North  lat.;  there- 
fore the  elevation  of  the  pole  is  always  equal  to  the  latitude  of  the 
place. 

It  will,  no  doubt,  be  noticed  that  twice  during  its  revolution 
around  the  pole  the  Pole-star  will  be  at  the  same  height  as  the 
pole  itself,  and  also  that  twice  it  will  be  on  the  meridian,  namely, 
above  and  below. 

The  Observation. — The  best  time  to  observe  the  Pole-star  is 
during  twilight,  the  same  as  any  other  star,  but  the  following  is  a 
good  illustration.  Supposing  that  it  is  the  intention  to  observe  the 
Pole-star  to  obtain  the  latitude  some  time  during  the  early  hours 
of  the  morning.  Proceed  as  follows:  About  the  time  that  the 
first  appearance  of  dawn  is  seen  in  the  sky,  bring  the  Pole-star  down 
to  the  horizon  and  clamp  the  sextant.  Then  wait  until  daylight, 
and  with  the  sextant  direct  the  sight  to  the  same  part  of  the 
horizon,  and  on  or  near  it  will  be  seen  the  star,  although  perhaps 
there  may  be  so  much  light  in  the  sky  that  the  star  will  not  be 
visible.  Make  the  contact  between  the  star  and  horizon  very  nicely, 
read  the  altitude,  and  note  the  time  on  board  of  ^hip  or  the  time 
by  chronometer  (G.M.T,).  You  then  proceed  to  find  the  latitude 
by  the  rule  here  given,  which  is  the  same  as  that  given  on  the  last 
page  of  the  American  Nautical  Almanac. 

Taylor's  Mod.   Nav.   6. 


82  TAYLOifs  Modern  Xavigatiox. 


EuLE. — Mark  down  the  ship's  tiiiie^  and  if  it  be  a.m.  add  12  to 
the  hours,  but  if  p.m.^  let  it  stand  as  it  is.  This  will  give  the 
astronomical  time  at  ship.  Enter  Table  3  of  the  Nautical  Almanac 
(which  is  a  table  for  converting  mean  solar  or  sun's  time  into 
sidereal  or  star  time)^.  with  the  hours  of  the  astronomical  time  on 
the  top  of  the  page  and  the  minutes  on  the  side.  Under  the  hours 
and  abreast  of  the  minutes  will  be  found  the  mean  time  interval, 
which  must  always  be  added  to  the  astronomical  time  at  ship.  Next, 
from  the  Nautical  Almanac,  on  page  2  of  the  month  and  abreast 
of  the  Greenwich  date,  take  out  the  sidereal  time,  or  right  ascen- 
sion of  the  mean  sun,  for  the  nearest  day.  Add  this  also  to  the 
ship's  time. 

It  is  sometimes  considered  necessary  to  correct  the  sidereal  time 
for  the  number  of  hours,  but  from  a  practical  point  of  view  it  is 
not  required,  owing  to  the  Pole-star  not  changing  its  altitude  very 
rapidly.  We  will  therefore  not  consider  this  correction  in  this  rule, 
but  will  assume  that  the  sidereal  time  taken  out  abreast  of  the  date 
is  the  correct  one  to  be  used. 

Now  convert  the  longitude  into  time,  and  with  this  time  enter 
Table  3  of  the  Nautical  Almanac,  with  the  hours  on  the  top  of  the 
page  and  the  minutes  on  the  side.  Under  the  hours  and  abreast 
of  the  minutes  will  be  found  the  interval,  to  be  applied  to  the  ship's 
time.  Subtract  this  interval  when  in  East  longitude  and  add  when 
in  West  longitude.  This  rule,  when  followed  out,  will  give  you 
the  local  sidereal  or  star  time  at  ship. 

To  Find  the  Star's  IIour-Anglc. 

{  less  than  P  20"M,  subtract  it  from  P  20"M; 
If  the  sider-    J    between  1^^  20"M,  and  13'^  20"M, subtract  1'^  20"M, 
eal  time  is      j        from  it; 

l^  greater  than  18'^  20'".1,  subtract  it  from  25"  20'". 1 ; 
and  the  remainder  is  the  hour-angle  of  the  Pole-star. 

Now  correct  the  observed  altitude  of  the  star  the  same  as  in  cor- 
recting the  altitude  of  any  star,  namely,  by  applying  the  LE.  of 
the  sextant,  the  refraction,  and  the  dip. 

Then  enter  the  table  here  given,  with  the  hours  on  the  top  of 
the  page  and  the  minutes  on  the  side,  and  take  out  the  correction,, 
which  must  be  applied  to  the  altitude  according  to  the  sign  pre- 
fixed to  it,  adding  when  the  -|-  sign  is  prefixed  and  subtracting  when 
the  —  sign  is  prefixed.  This  will  give  the  latitude,  to  be  named. 
North  always. 


]\Iehidiax  Altitude. 


83 


The  table  of  hour-angles  given  here  is  only  for  working  the 
questions  contained  in  this  book,  and  for  the  observations  taken 
during  the  year  of  1894.  When  making  ohservations  for  yourself, 
use  the  table  of  hour-angles  given  in  the  American  Nautical  Al- 
manac of  the  current  year.  The  reason  for  this  is  that  the  con- 
stant numbers  change  from  vear  to  vear. 


TABLE  lY.— 1894. 


Hour- 
Angle. 

0" 

1'^ 

2" 

8" 

4" 

5'' 

m 

0 

5 

10 
15 

20 
25 
30 
35 

40 
45 
50 
55 
60 

115.3 

0.2 

113.6 
113.2'-' 
-112.S'-' 

-112.8;, 
112.4 

111-9  ■ 

111.4"-j' 

-110.8''' 
110-2  • 
1    9.B 
1    8.9"-' 

0.7 

"\ !?:; 

m 

1.11 

-}  Ik 

-057.4]'[, 
0  56.4  -'; 

0  55.2  ■; 

0  54.1  ■' 
0  52.9- 

-0  52.9.,', 

0  51.7  •: 

0  50.5  •; 

0  49.3 

-0  48.0 1' 
0  46.7  • 
0  45.4  - 
0  44.1'-' 

1.4 

-0  42.7,, 
0  41.3  • 
0  39.9  ■' 
0  38.5,-^ 
037.1" 

-0  37.1  ;^ 
0  35.6  •, 
0  34  2; 
0  32.7'-' 

-031.2''^ 

0  29.7- 

0  28.2  -^ 

0  26.6'-' 
1.5 

-0  25.1    ^ 
0  23.5  • 
0  21.9- 
0  20.3  -' 

-018.7'-*' 

-018.7  '^ 

017.1  • 

015.5  • 

013.9 
1.6 

-012.3,. 

010.7- 

0   9.0  • 

0   7.4'-' 

1.6 

-0   5.8,^ 

0   4.1  ■ 

0   2.5  • 

-0   0.8  • 

0   0.8'-' 

Hour- 
Angle. 

6'^ 

7h 

8" 

9" 

10" 

IV' 

m 

0 

5 

10 

15 

20 
25 
30 
35 

40 
45 
50 
55 
60 

+0   0.8  '. 

0  2.5  -;. 

0   4.1 

0  5.7|-;: 

0   9.0  -^ 
010.7  -' 

012.3'-' 

i.fi 

+013.9^, 
015.5 
017.1  ■ 
018.7  - 

+0  20.3 

-0  20.3  '^ 
0  21.9  -' 
0  23.4  - 
0  25.0^-' 

1.5 

-0  26.5 , , 
0  28.1  - 
0  29.6  ■! 
0  31.1  -' 

^0  32.6]'; 
0  34.0   ! 
0  35.5  •; 
0  36.9  •' 
0  38.3 

:  0  38.3,' 
0  39.7  -' 
041.1  -, 
0  42.5  '- 

+0  43.8[t 

0  45.1  •; 

046.4  i 

0  47.7'-;; 

-0  49.o'"| 

0  50.2  -; 

051.4  ':, 

0  52.6  ■" 

-0  53.7'-' 

0  53.7  '„ 
0  54.9;; 
0  56.0  - 
057.1'-' 

1.0 

4  0  58.1,^ 

0  59.1  • 

1  0.1  -" 
1    1.1  ;^^ 

'1    2-1 11 

1  III- 

i  ^ 

1    7.8  - 

0.7 

4-1    8.5^^ 

1  -:: 

110.4"-; 

■i  12.9" 

-112.9;, 

113.3- 

113.7  • 

114.0"-' 
0.3 

^  114-3  OS 
114.6- 

114-8-.^ 
1  15.0    " 

0.1 

.1  15.1  ^, 

-lit!" 

84  Taylor's  Modern  Navigation. 

Example.— ^ovemhev  10,  1894,  at  9^  29"^  29«  p.m.,  M.T.S.;  long. 
29°  E.;  T.  alt.  Pole-star  29°  29'  00".     Find  the  latitude. 

Mean  time  ship,  9'^  29'"  29« 

Sidereal  interval.  Table  3,  N.A.  +   1     34 

Sidereal  time,  or  R.A.  of  mean  )  ^^    -j^g     g-j^ 

sun,  page  2  of  month,  ' 

Long.  29"  E.  49     34 


4 
60)116 

1'^  56™ 

(From  Table  3.) 

-19 

00   49    15 
1    20    06 

Hour-angle  Pole-star,    0'^  30'"  51« 

T.  alt.  Pole-star,    29°  29' 00"  (Cor.  for  dip  and  ref.) 
Cor.  from  table,    -1    14  48 


Lat.  of  ship,  28°  14'  12"  N. 

The  above  question  is  taken  from  the  Nautical  Almanac  for  1894. 

Exaiu ph.— ^OYvmhei  12,  1894,  p.m.  at  ship;  long.  35°  28'  W.; 
chron.  November  12*^  13^  40"^  10^  M.T.G. ;  obs.  alt.  Pole-star 
64°  28'  30";  I.E.  00'  00";  height  of  eye  25  feet.  Find  the  lati- 
tude. 

Chron.  Nov.  12'^  13'^  40'"  10^  M.T.G.  Long.  35°  28'  W 

-  2    21     52  4 


12    11    18     18    M.T.S.  60)141    52 

Sidereal  interval,       +  1     51    (Table  3.)  2''  2P"  52^ 

R.A.,    or  sidereal 


,   +15    30     21    N.A. 
time  nearest  day,  ) 

Interval  for  W.  long.  +  23 


Sidereal  time  at  ship,     2    50     53 
-   1    20     06 

Hour-angle,                      1"  30"'  47« 

Obs.  alt.  64°  28'  30" 
-  5  22 

Dip,  4'  54' 
Ref.       28 

T.  alt.       64    23  08 
-1    09   30 

—5'  22' 

Latitude, 63°  13'  38"  N. 


Meridian  Altitude. 


85 


Examples. 

1894,  February  6th,  1''  -iy""  a.m.,  M.T.S.;  long.  45°  26'  W. ;  obs. 
alt.  Pole-star  56°  5i)'  40";  I.E.  —1'  15";  eye  12  ft.  Find  the  lati- 
tude. 

Answer. — 57°  55'  53"  j^. 
1894,  January  22d,  2^  10°^  a.m.,  M.T.S.;  long.  52°  W.;  obs.  alt. 
Pole-star  48°  54'  00";  I.E.  -f20'  10";  eye  10  ft.   Find  the  latitude. 
Answer.— 50°  03  55"  X. 
1894,  April  Tth,  p.m.  at  ship;  long.  150°  E.;  chron.  April  1^  1^ 
40'"  16^  M.T.G.;  obs.  alt.  Pole-star  46°  59'  50";  I.E.  00';  eye  24 
ft.     Find  the  latitude. 

Answer.— 48°  08'  44"  X. 
1894,  November  22d,  7'^  50™  p.m.,  M.T.S.  ;  long.  160°  10'  W.; 
obs.  alt.  Pole-star  57°  48'  10";  I.E.  00';  eye  20  ft.    Find  the  lati- 
tude. 

Answer.— 56°  32'  29"  X. 
1894,  December  25th,  7^^  10""  12«  p.m.,  M.T.S. ;  long.  18°  40'  E. ; 
obs.  alt.  Pole-star  35°  10'  20";  I.E.  00';  eye  14  ft.     Find  the  lati- 
tude. 

Answer.— 33°  49'  53"  X. 


Pole  ^tar  Probleh 


Let  0  be  place  of  observer. 

X  S  observer's  horizon,  0  Z  observer's  meridian. 


86  Taylor's  Modern  Navigation. 


Z  Zenith,  and  the  circle  A  C  B  D  the  path  of  the  Pole-star,  P 
the  Pole  itself. 

As  the  elevation  of  the  Pole  is  equal  to  the  latitude  of  the  place, 
the  following  will  enable  the  student  to  understand  it. 

By  studying  the  diagram  it  will  be  evident  that  twice  during  the 
day  the  Pole-star's  altitude  will  be  the  same  as  the  Pole  itself, 
namely,  when  it  is  at  the  points  A  and  B,  in  either  of  these  posi- 
tions, its  correct  altitude  is  equal  to  the  latitude. 

When  at  D  it  is  on  the  meridian  below  the  Pole,  and  when  at  C 
on  the  meridian  above  it. 

If  the  star  is  in  the  lower  semicircle,  viz. :  B  D  A,  the  correction 
must  always  be  added  to  the  altitude  to  obtain  the  latitude,  but 
when  in  the  semicircle  A  C  B,  it  must  be  subtracted. 

For  the  solving  of  this  problem,  see  rule. 


DIVISION  IV. 

LATITUDE  BY  EX  MERIDIAN  ALTITUDE  OF  THE  SUN, 
OH  DEDUCTION  TO  THE  MERIDIAN. 

When  the  sun  is  obscured  at  noon  by  reas^on  of  cloudy  weather,  it 
is  impossible  to  find  the  latitude  by  meridian  altitude.  In  such  a 
case  the  latitude  must  be  found  by  the  reduction  to  the  meridian 
method. 

The  Observatipn. — Within  one  hour  of  noon  at  ship  (the  nearer 
to  noon,  the  better)  observe  the  sun's  altitude  and  note  the  time  by 
chronometer,  or  the  correct  apparent  time  at  ship ;  then  proceed  by 
the  following  rule. 

EULE. 

First  Case. — To  find  Greenwich  time  if  ship's  time  is  given.  To 
the  time  by  watch  apply  the  error  for  apparent  time  at  ship ;  add  if 
slow,  subtract  if  fast.  Then  apply  the  difference  of  longitude  in 
time;  add  if  East,  subtract  if  West.  The  result  will  be  the  A.T.S., 
to  which  apply  the  longitude  in  time;  if  East,  subtract;  if  West, 
add.  The  result  will  then  be  the  Greenwich  apparent  time 
(G.A.T.). 

Second  Case. — If  G.M.T.  is  given.  To  the  time  by  chronometer 
apply  the  error,  if  any.  This  is  the  G.M.T.  Convert  the  longitude 
into  time ;  adding  if  East,  subtracting  if  West.  The  result  will  be 
the  ship's  mean  time  (S.M.T.).  Take  the  equation  of  time  from 
the  Nautical  Almanac,  page  2,  and  correct  for  the  G.M.T.  and 
apply  it  to  the  S.M.T.,  as  stated  on  top  of  the  column.  The  result 
will  be  the  apparent  time  at  ship  (A.T.S.). 

To  Find  the  Time  from  Noon. —  If  p.m.  at  ship,  tlie  minutes  and 
seconds  of  A.T.tS.  will  be  the  time  from  noon.  If  a.m.  at  ship,  sub- 
tract the  hours,  minutes,  and  seconds  of  A.T.S.  from  24  hours,  and 
the  remainder  will  be  the  time  from  noon.  Correct  the  declination 
for  the  Greenwich  time,  and  correct  the  altitude. 

To  Find  the  Approximate  Meridian  Altitude  (Approx.  Mer. 
Alt.). — Mark  down  the  correct  declination,  and  under  it  put  the 
latitude  by  account.  If  they  are  different  names,  add;  if  the  same 
name,  subtract.     Then  subtract  the  result  from  90°.     The  remain- 


S8  Taylor's  Moderx  Xavigatiox. 

der  will  be  the  approx.  mer.  alt.  Under  the  approx.  mer.  alt.  put  the 
T.  alt.  Add  them,  and  divide  the  sum  by  2.  The  remainder  is 
the  half-sum  of  the  approx.  mer.  alt.  and  the  T.  alt. 

The  Worhing. — Add  together  the  cosine  of  the  latitude  by  ac- 
count, cosine  of  the  correct  declination,  twice  the  sine  of  the  time 
from  noon,  taken  from  the  p.m.  column  always,  and  the  secant  of 
half  the  sum  of  the  approx.  mer.  alt.  and  the  T.  alt.  The  sum 
is  the  sine  of  one  half  the  correction,  to  be  added  to  the  T.  alt.  to 
obtain  the  mer.  alt. 

Then  subtract  the  corrected  altitude  from  90°.  The  remainder 
will  be  the  Z.D.,  to  be  named  opposite  to  the  suns  bearing.  Under 
the  Z.D.  put  the  correct  declination,  adding  if  same  name,  sub- 
tracting if  different  names.  The  remainder  is  the  latitude,  to  be 
named  the  same  as  the  greater. 

Reduction  to  the  Meridiax  by  Towson^s  Method. 

This  method  is  immensely  superior  to  any  other,  for  the  reasons 
that  it  is  extremely  simple,  and  that  it  is  independent  of  the  lat- 
itude by  account.  But  there  is  a  limit  to  it,  when  the  altitude  and 
declination  are  both  large;  that  is.  when  the  sun  is  on  the  same 
side  of  the  equator  as  the  observer;  but  as  it  is  winter  when  the 
navigator  needs  this  problem  the  most,  he  need  not  worry  about 
the  limit.  If,  when  working  Towson's  method,  you  find  that  you 
are  outside  the  limit  of  the  table,  you  must  fall  back  upon  the 
Bowditch  rule. 

Towson's  Rule. — Correct  the  altitude  and  declination  and  find 
the  time  from  noon,  as  in  the  Bowditch  method. 

Enter  Table  1  with  the  declination  on  top,  and  the  time  from 
noon  in  the  hour-angle  column,  and  take  the  correction  abreast  of 
it  and  add  it  to  the  corrected  declination  always.  Take  the  index 
number  abreast  of  the  correction  and  mark  it  down.  Then  enter 
Table  2  with  the  altitude  on  top  and  the  index  number  at  the  side, 
and  under  the  altitude  abreast  of  the  index  number  will  be  found 
the  correction,  to  be  added  to  the  T.  alt.  always.  Subtract  the  in- 
creased altitude  from  90°  and  find  the  Z.D.  Name  the  Z.D. 
opposite  name  to  the  bearing.  Apply  the  increased  declination 
and  find  the  latitude  by  the  same  rule  as  in  the  meridian  altitude. 

The  latitude  found  will  be  the  latitude  of  the  sliip  at  the  time 
of  observation,  noi  for  noon,  unless  the  ship  has  bei'n  standing  still 
between  the  observation  and  noon. 


Meridian  Altitude. 


89 


Example— 1S94.  August  5t>a.  r.M.  at  ship,  in  lat.  44°  00'  X. 
and  long.  119°  40'  W.  by  ace;  obs.  alt.  of  sun's  L.L.  57°  20'  00", 
bearing  S. ;  I.E.  — 12'  10":  height  of  eye  20  feet;  time  by  chron. 
August  22'^  S^  20'"  40«,  which  was  2"^  8''  fast  of  G.M.T.  Requin-d 
the  latitude. 


Chron. 


Aug.  22"  8"  20'"  40« 
-   2       8 


G.M.T.  22    8    18     32 

Sub.,  because  W.,  -   7    58     40 

S.M.T. 
Cor.  equa. 

S.A.T.  22"  0'^  17"^  14^ 


Long.  119°  40'  W. 
4 


60)478    40 
Long,  in  time, 


58"^  40« 


22   0    19     52 

2     38 Equa.  N.A.,  p.  2  of  month. 

2"^  43^27  0.632  H.D. 

-5  .24 8.3 


Equa.  of  time  cor.  for  G.M.T. 


— 2"^  38^.03 


1896 
5056 

-5^2456 


Decl.          11°  42'  43"  N. 
-  6  59 


Cor.  decl.  11°  35'  44"  N. 


50".56  H.D. 

S.3   (hrs.  and  tenths  of  G.M.T.) 

15168 
40448 


60)419.648 


6'  59" 


Obs.  alt.  57°  20'  00"  S. 

Parlx.  0'  4" 

LE.  12' 10' 

-  1  15 

S.D.   15  52 

Dip,  4  23 

Cor.  alt.  57°  IS'  45" 

+  15' 56" 

Ref.    38 

-17  11 
+  15  56 

1'  15' 


90  Taylor's  Modern  Navigation. 


Lat.  by  ace.         =44''  00'  00"  N. 
Cor.  decl.  =11    35  44    N. 


Approx.mer.alt.  =  57    35  44      Sine  for  17'"  12%  as  it 
Cor.  alt.  =57     18  45  is  nearest  to  17"M4% 


32 

90 

24  16 
00  00 

.=57 
=  57 

35  44 

18  45 

})114 

54  29 

:8.57421 

X2 


Rejecting  10,  ,-7.14842 


Half-sum  of  alts.  =  57°  27'  14" 


Cosine  lat.  by  ace.  44°  00'  N.  =  9.85693 

Cosine  cor.  decl.  11    36  N.  =  9.99104 

Twice  sine  time  from  noon,         17"^  14^       =  7.14842- 
Secant  half-sum  of  alts.  57°  27'        =10.26919 

Rejectingthetens,thesum  isthesineof  half-  ) 

reduction,  )    7.26558  =  6'  nearly 

X2 

Reduction,  to  be  always  added  to  cor.  alt.  +12' 

Cor.  alt.        57°  18'  45"  bearing  S. 
Reduction,      +  12  00 

Reduced  alt.  57    30  45 
90    00  00 


Z.D.  32    29  15    N. 

Cor.  decl.       11    35  44    N. 

Latitude,       44°  04'  59"  N. 

This  example  is  worked  to  nearest  minutes  of  arc  only,  in  the 
logs. 

Same  Problem  by  Towson's  Ex  Meridian  Tables. 

The  A.T.S,  must  be  found,  to  obtain  the  hour-angle,  or  time 
from  noon;  also,  the  decl.  and  alt.  must  be  corrected  as  in  the 
Epitome  method. 

/Give  1'  59"  (from  Table  1),  to 

,,  _  \        be  added  to  cor.  decl.,  and 

H.A  1,-  14»  =  nearest  17»9'  ^^^^^^^  ^^  ■      ;„   ^j,,^  ^„i. 

Cor. decl.  11°  35'=nearestl2°  „^„_   ;,   j„„,;,,   „,,   i„j^, 

I         number,  namelv,  35. 


Mekiuian  Altitude.  91 

Cor.  decl.  11°  85'  44"  N. 

+  1   59 


Augmented  decl.  11°  37'  43"  N. 

Alt.  57°  30'  )  Give,   when    interpolating,    14'    35"   (from 

Index     number,  35    i       Table  2),  to  be  added  to  the  cor.  alt. 

Cor.  alt.  57°  18'  45"  S. 

+  14  35 


Augmented  alt.    57    33   20    S. 
90    00  00 


Z.D.  32    26  40    N. 

Augmented  decl.  11    37  43    N. 

Latitude,  44°  04'  23"  N. 

Example— 1894,  September  16th,  a.m.  at  ship,  in  lat.  20°  10'  S. 
and  long.  140°  2'  E.  by  ace;  obs.  alt.  of  sun's  L.L.  66°  50', 
bearing  N. ;  I.E.  00'  00" ;  height  of  eye  29  feet ;  time  by  watch 
Sept.  15"^  22^  40™  50%  which  has  been  found  to  be  slow  V  S*"  10« 
on  A.T.S. ;  diff.  of  long,  made  to  the  West  was  16'  since  the  error 
on  A.T.S.  was  determined.  Required  the  latitude  by  reduction 
to  the  meridian.  '        '' 

Sept.  15-^  22^^  40'"  50^        D.  long.  16'  W.     Long.  140°  2'E 
Slow  of  A.T.S.      +   1      2    10  4  4 


Decl. 

Cor.  decl.  =2°  42'  17"  N 


15  23  43 

00 
4 

60)64       60)560  8 

-  1 

1-  4«       g*'  20'"  8» 

S.  15  23  41 

56 

24"  00"^  00« 

-  9  20 

8 

23  41  56  A.T.S. 

G.  15^  U^  21" 

M8« 

Igm  4s  (xi^g  fj.on-j  noon.) 

57".79  H.D. 
14.4 

23116 

23116 

5779 

2°  56'  09"X. 

60)832.176 

13  52 

13'  52" 

92 


Taylor's  ^Modkrx  Xav 


aOATIOX. 


8.D. 

Pari. 


Obs.  alt.  66°  50'  00' 

+  10  19 

T.  alt.      67°  00'  19" 


15'  57" 

4 

+  16  01 
-  5  42 


Dip,  5'  17' 
Ref.       25 


-5'  42' 


10'  19" 


Lat.  ace. 
Cor.  decl. 


20°  10'  8. 
2    42  N. 


22    52 
90    00 


Approx.  mer.  alt.  67 
T.  alt.  67 


Sine  18" 


4«  =8.59395 
X  2 


Half- sum  alts.      67°  04' 

Cosine  lat.  ace. 

Cosine  cor.  deel. 

2 X sine  time  from  noon,    18'"    4^^ 


20°  10'  S. 

2°  42' N. 


2Xsine  =7.18790 

9.97252  I 

9.99952  I 


Secant  half-sum  alts. 


67°  04' 


T.  alt. 


67°  00'  19"  N. 

+  26 


=  7.18790 

=  10.40931 

7.56925=13' 

X_2 

Reduction,  4-26 


67 

26 

19 

90 

00 

00 

Z.D. 

22 

33 

41 

Cor. 

decl. 

2 

42 

17 

Latitude,  19°  51'  24"  8. 

Sainc  Problem  by  Towsons  Method. 


H.A.   18'»  4-^ 
Cor.  decl.  2°  42'  17"  N. 
+  23 


Index  number  41. 
T.  alt.        67°  00'  19"  N. 

+  25  44 


2°  42'  40"  N. 


67    26  03 
90    00  00 


Z.D.  22    33  57    8. 

Cor.  decl.     2    42   40    N. 

Latitude,    19°  51'  17"  S. 


Meridian  Altitude.  93 


Exam  pies,  fur  Practice. 

1894,  August  (Uh,  a.im.  at  ship,  in  lat.  47°  50'  S.  and  long.  85°  15' 
W.  by  ace;  sun's  obs.  alt.  L.L.  Ji5°  25'  00'',  bearing  N.;  I.E.  — 5' 
40";  eye  23  ft.;  time  by  chron.  (S'^  5"  47""  50%  which  was  Ifi"" 
47^  fast  of  G.M.T.  Find  the  latitude  by  reduction  to  the  merid- 
ian. 

Answer.— G.M.T.  August  G'l  b""  'dV"  03«;  S.M.T.  5^'  W  50"' 
03*;  A.T.S.  Q^  23"  44'"  22^;  c<iua.  5'"  41«;  time  from  noon  15'" 
38*;  cor.  decl.  16°  35'  08"  N. ;  T.  alt.  25°  28'  39" ;  approx.  mer.  alt. 
25°  35';  sine  Vo  red.  6.91675;  reduction  6';  lat.  47°  50'  13"  S.       - 

Answer  by  Towson's.— Aug.  dccl.  16°  37'  23"  N.;  aug.  alt. 
25°  32'  11";  lat.  47°  50'  26"  S. 

1894.  September  24th,  p.m.  at  ship,  in  lat.  49°  56'  S.  and  long. 
37°  40'  E.  by  ace;  sun's  obs.  alt.  L.L.  40°  20'  20",  bearing  X. ; 
I.E.  +2'  10"  :  eye  10  ft. ;  time  by  chron.  23^  22"  40™  10%  which 
was  55""  18*  fast  of  G.M.T.  Find  the  latitude  by  reduction  to 
the  meridian. 

Answer.— A.T.S.  24*^  00"  23'"  34*;  time  from  noon  23°'  34*; 
cor.  decl.  0°  31'  31"  S. ;  ecpui.  4-8'"  00*;  T.  alt.  40°  34'  22";  ap- 
prox. mer.  alt.  40°  36';  sine  i/o  red.  7.35116;  reduction  +16';  lat. 
49°  41'  09"  S. 

Answer  by  Towson's.— Lat.  49°  41'  36"  S. 

1894,  October  4th,  p.]\r.  at  ship,  in  lat.  49°  56'  S.  and  long. 
130°  40'  W.  by  ace;  sun's  obs.  alt.  L.L.  44°  36'  00",  bearing  N. ; 
I.E.  +7'  10" ;  eye  26  ft. ;  time  by  watch  October  4^1  1"  40""  10*, 
which  was  56'"  5*  fast  of  A.T.S.;  diff.  of  long,  made  to  the  East 
17'  since  the  error  of  watch  was  determined.  Find  the  latitude  by 
reduction  to  the  meridian. 

Answer.— A.T.S.  4'^  0"  45'"  13«;  G.A.T.  4<'  9"  27""  53*; 
time  from  noon  45'"  13*;  cor.  decl.  4°  36'  08"  S.;  sine  1/2  red. 
7.94259;  reduction  60';  lat.  48°  42'  48"  S. 

Outside  the  limit  of  Towson's  Tables. 

1894,  ISTovember  5th,  p.m.  at  ship,  in  lat.  14°  56'  N.  and  long. 
101°  21'  E.  by  ace;  sun's  obs.  alt.  L.L.  59°  20'  00",  bearing  S. ; 
I.E.  —1'  40";  eye  21  ft.;  time  by  watch  5"^  1"  20"*  40%  which 
was  fast  of  A.T.S.  1"  5""  15*;  diff.  of  long,  made  to  the  East 
40'  since  the  error  of  watch  was  determined.  Find  the  latitude  by 
reduction  to  the  meridian. 

Answer.— A.T.S.  5<^  0"  18'"  5*;  A.T.G.  4'^  17"  32-"  41*;  time 
from  noon  18""  5*;  cor.  decl.  15°  41'  34"  S. ;  T.  alt.  59°  29'  31"; 
sine  1/2  red.  7.45654;  lat.  14°  28'  55"  N. 


94  Taylor's  Modern  Navigation. 


Answer  by  Towson's. — Lat.  l-i°  28'  57"  X. 

1894,  December  14th,  a.m.  at  ship,  in  lat.  46°  40'  S.  and  long. 
20°  40'  E.  by  ace;  sun's  obs.  alt.  L.L.  66°  18'  00",  bearing  N.; 
I.E.  —2'  15";  eye  30  ft.;  time  by  chron.  December  IS'^  22^  5°^ 
18«,  which  was  2""  10«  fast  of  G.M.T.  Find  the  latitude  by  re- 
duction to  the  meridian. 

Answer.— A.T.S.  13<i  23^^  30™  55«;  time  from  noon  29""  5«; 
cor.  decl.  23°  14'  24"  S.;  sine  1/2  red.  7.80283 ;>t.  46°  04'  06"  S. 

Outside  the  limit  of  Towson's  Tables. 

1894,  March  30th,  p.m.  at  ship,  in  lat.  42°  29'  N.  and  long. 
140°  40'  E.  by  ace;  sun's  obs.  alt.  L.L.  50°  57'  20",  bearing  S.; 
I.E.  —1'  10";  eye  20  ft.;  time  by  chron.  March  30^  1^  lO'"  15% 
which  was  51""  2«  fast  of  A.T.S. ;  diff.  of  long,  made  to  the  East 
17'  since  the  error  on  A.T.S.  was  found.  Find  the  latitude  by 
reduction  to  the  meridian. 

Answer. — Time  from  noon  20™  21^;  cor.  decl.  3°  43'  39"  N.; 
T.  alt.  51°  07'  04",  corrected  by  table;  sine  7.36622;  lat.  42°  20' 
35"  N". 

Answer  by  Towson's.— Lat.  42°  20'  35"  N. 

1894,  May  22d,  a.m.  at  ship,  in  lat.  53°  50'  S.  and  long.  179'* 
]8'  W.  by  ace;  sun's  obs.  alt.  L.L.  15°  28'  10",  bearing  N.;  I.E. 
+5'  15";  eye  12  ft.;  time  by  chron.  May  22'»  5^  47™  30%  which 
was  6^  10™  10«  fast  of  A.T.S.;  diff.  of  long,  made  to  the  East 
12'  since  the  error  on  A.T.S.  was  determined.  Find  the  latitude  by 
reduction  to  the  meridian. 

Answer.— Time  from  noon  21™  52«;  T.  alt.  15°  42'  37";  cor. 
decl.  20°  32'  08"  N.;  lat.  53°  36'  15"  S. 

Answer  by  Towson's.— Lat.  53°  36'  27"  S. 

1894,  November  1st,  a.m.  at  ship,  in  lat.  42°  18'  X.  and  long. 
51°  10'  W.  by  ace;  sun's  obs.  alt.  L.L.  33°  2'  30".  bearing  S.; 
I.E.  00'  00";  eye  16  ft.;  time  by  chron.  Nov.  1'^  1^  10™  50%  which 
had  been  found  to  be  V  47™  10«  fast  on  A.T.S.;  diff.  of  long, 
made  to  West  17'  since  the  error  on  A.T.S.  was  determined.  Find 
the  latitude  by  reduction  to  the  meridian. 

Answer.— Lat.  41°  33'  56"  X.  by  Bowditch. 

Lat.  41°  32'  36"  X.  by  Towson's. 

1894,  October  30th,  p.m.  at  ship,  in  lat.  28°  49'  S.  and  long.  166° 
50'  W.  by  ace ;  sun's  obs.  alt.  L.L.  75°  4'  10",  bearing  N. ;  eye  26  ft. ; 
time  by  watch  October  30<^  11^'  16™  5%  which  was  fast  10^  of 
G.M.T.    Find  the  latitude  by  reduction  to  the  meridian. 

Answer.— Lat.  27°  39'  41"  S. 


Meridian  Altitude.  95 


1894,  July  12th,  p.m.  at  ship,  in  lat.  3(i°  49'  S.  and  long.  174°  20' 
E.  by  ace; "^ sun's  obs.  alt.  L.L.  30°  54'  10".  bearing  X.;  I.E. 
—3' 10";  eye  30  ft.;  time  by  chron.  July  ll'>  12"  40'"  8",  which  was 
IB-"  40^  slow  of  G.M.T.  Find  the  latitude  by  reduction  to  the 
meridian. 

Answer.— Lat.  36°  30'  53"  S. 

1894,  June  11th,  a.m.  at  ship,  in  lat.  47°  20'  S.  and  long.  120°  4' 
E.  bv  ace;  sun's  obs.  alt.  L.L.  19°  22'  30",  bearing  N. ;  I.E. 
+7'  20" ;  eye  20  ft. ;  time  by  chron.  June  10^  15^  40""  10«.  which 
was  I'"  41^  slow  of  G.M.T.  Find  the  latitude  by  reduction  to  the 
meridian. 

Answer.— Lat.  47°  9'  49"  S. 

1894,  May  28th,  p.m.  at  ship,  in  lat.  49°  20'  N.  and  long.  100°  20' 
E.  bv  ace;  sun's  obs.  alt.  L.L.  61°  52'  10",  bearing  S. ;  LE. 
H-3'"l0" ;  eye  12  ft. ;  time  by  watch  May  28<^  &'  40™  10%  which  had 
been  found"^  to  be  6"  lO""  5^  fast  of  A.T.S. ;  ditf.  of  long,  made 
to  the  East  20'  since  the  error  on  A.T.S.  was  determined.  Find 
the  latitude  by  reduction  to  the  meridian. 

Answer.— Lat.  48°  38'  42"  N. 

KEMAEKS     OX     THE     METHOD     OF      FIXDIXG      THE 
LATITUDE  BY  EX  MERIDIAX  ALTITUDE. 

*  It  is  very  necessary  for  the  student  to  understand  thoroughly 
that  the  latitude  found  by  any  of  the  rules  in  this  section  is  the 
latitude  of  the  ship  at  the  time  the  sight  was  taken,  and  if  the 
latitude  be  required  for  some  other  time,  it  must  be  corrected  for 
the  difference  of  latitude  the  ship  has  made  on  the  true  course  and 
the  distance  the  ship  sailed  in  the  interval. 

It  will  be  noticed  that  the  times  given  are  somewhat  different, 
and  as  a  correct  knowledge  of  the  time  is  very  important,  we  will 
here  give  an  explanation. 

First  Case.— When  error  is  given  on  apparent  time  at  ship  with 
a  difference  of  longitude. 

Suppose  it  is  the  intention  to  observe  the  sun's  altitude  to  ob- 
tain the  latitude  by  reduction  to  the  meridian. 

Find  the  error  of  the  chronometer  on  apparent  time  at  ship  in 
the  following  manner,  previous  to  the  sight : 

Calculate  the  longitude  the  ship  will  be  in  at  the  intended  time 
of  observation,  convert  it  into  time,  and  mark  it  minus  ( — )  if 
West  longitude,  and  plus  (  +  )  if  East  longitude.     Xext,  take  from 


96  Taylor's  Modern  Xavigation. 


page  2  of  the  Nautical  Almanac  the  equation  of  time  and  correct 
it  for  G.M.T.  and  mark  it  +  or  — ,  according  to  the  sign  on  top 
of  column;  then  take  the  sum  of  the  longitude  in  time  and  the 
corrected  equation  if  they  are  both  4-  or  both  — ,  or  the  differ- 
ence if  one  is  +  and  the  other  — .  The  result  in  either  case  will 
be  the  error  of  the  chronometer  or  watch  on  apparent  time  at  ship, 
to  be  applied  to  the  noted  time  by  chronometer  or  watch  according 
to  its  sign,  to  obtain  the  A.T.S.  at  observation.  Now,  if  the  sun 
be  not  observed  at  the  time  intended,  this  A.T.S.  must  be  again 
corrected  for  the  diff.  of  long,  the  ship  made  between  this  time  and 
the  time  of  actually  taking  the  observation  to  obtain  the  correct 
apparent  time  at  ship,  and  thence  the  hour-angle,  or  time  from 
noon. 

Second  Case. — When  the  time  by  chronometer  is  noted,  and,  by 
the  way,  this  is  the  easiest  method  to  understand.  Measure  the 
sun's  altitude,  and  note  time  by  chronometer,  and  proceed  to  find 
the  A.T.S.  by  the  rule  given. 

For  Practice  at  Sea. — Set  your  watch  to  A.T.S.  for  noon,  com- 
pare watch  with  chronometer,  and  mark  down  the  times. 

Turn  long,  of  ship  by  D.R,  into  time,  and  add  it  to  correct 
G.M.T.  if  in  East  longitude,  and  subtract  if  in  West  longitude. 
The  result  will  be  M.T.S.  Take  the  equation  of  time  from  page 
2  of  the  Nautical  Almanac  and  correct  it  for  G.M.T.,  then  apply 
the  cor.  equa.  to  M.T.S.  according  to  its  sign,  and  the  result  will 
be  A.T.S.  at  instant  of  comparing  the  watch  with  chronometer. 

Set  the  watch  ahead  or  back  according  to  whether  slow  or  fast. 
You  will  then  have  A.T.S.  on  your  watch.  Make  the  observation 
and  note  the  time  by  watch.  This  will  be  the  A.T.S.  at  time  of 
observation.  If  it  is  an  a.m.  sight,  subtract  what  the  watch  shows 
from  12  hours,  and  the  remainder  will  be  the  time  from  noon;  but 
if  P.M.,  the  minutes  and  seconds  will  be  the  time  from  noon.  These 
wrinkles,  we  opine,  will,  in  conjunction  with  the  rules,  enable  the 
student  to  put  the  method  into  actual  practice. 

LATITUDE  BY  EX  MERIDIAN  OF  A  STAR. 

The  working  of  the  problem  is  essentially  the  same  as  the  sun 
problem,  with  the  exception  of  determining  the  star's  hour-angle. 

Rule  to  Find  the  Hour-Angle. 

Mark  down  the  astronomical  mean  time  at  ship  if  given,  omit- 
ting the  date. 


Meridian  ALTiTiibEV ^^ '  V' l ; :  ^t;/ T Y  ^7 


If  (i.M/r.  is  given,  namely,  time  by  clirouometer,  apply  to  it 
the  longitude  in  time,  adding  if  East,  subtracting  if  West.  The 
result  will  be  the  M.T.S. 

From  page  2  of  the  Nautical  Almanac  take  out  the  sidereal  time, 
iiiean-  noun,  and  correct  it  for  the  M.T.G.  by  using  Table  3  of 
the  Xautical  Almanac  for  converting  mean  solar  into  sidereal  time. 

Add  this  corrected  sidereal  time  to  the  astronomical  mean  time 
at  ship.  The  result  will  be  the  right  ascension  of  the  meridian 
(R.A.  of  mer.). 

Take  the  difference  between  the  R.A.  of  mer.  and  the  star's 
R.A.  (which  is  found  abreast  of  the  star's  declination  under  the 
lieading  of  Fixed  Stars,  in  the  Nautical  Almanac,  correcting 
it  for  the  annual  change  if  it  is  large,  but  ignoring  it  entirely  if 
small).    The  remainder  will  be  the  star's  hour-angle  (H.A.). 

Correct  the  altitude  as  in  other  star  problems.  Take  out  the 
star's  declination. 

Compute  the  approximate  meridian  altitude,  and  finish  the 
problem  the  same  as  when  working  latitude  by  ex  meridian  of  the 
sun. 

LATITUDE  BY  EX  MERIDIAN  ALTITUDE  OF  A  PLANET. 

The  problem  is  worked  the  same  as  a  star  problem,  with  the  ex- 
ception of  correcting  the  planet's  declination  and  right  ascension. 

Example.— 1S94:,  April  8th,  a.m.  at  ship,  in  lat.  20°  30'  N.  and 
long.  115°  50'  E.  by  D.R.;  obs.  alt.  star  Vega  71°  25'  N.;  I.E. 
+5'  20";  dip  22  feet;  time  by  chronometer  April  7^  9^*  26°^  0% 
which  was  slow  2^"  15^  for  G.M.T.  Required  the  latitude  by  ex 
meridian  altitude. 


April 

7.1     gh 

26'" 

0« 

+ 

2 

15 

G.M.T. 

9 

28 

15 

+  7 

43 

20 

S.M.T. 

+  17 

11 

35 

From  N.A. 

+  1 

2 

59  1 

+ 

1 

33 

R.A.  of  mer. 

18 

16 

07 

R.A.  starVega,  18 

33 

21 

Star's-hour  angle, 

17" 

1  14s 

Taylor's  Mod.  ] 

SlAV.  7. 

Long.  115°  50'  E. 
4 


60)463    20 


71,  43m  20« 


59  sid.  time  mean  noon. 
1     33  (Interval,  Table  3,  N.A.,  for  M.T.S.) 


Taylor's  Moderx  Xavigatiox. 


Lat.  by  D.R.        20°  30' 00"  N.  Star's obs.  alt. 71°  25' 00"  Dip,  4' 36' 
N.  +  0  24    Ref.     20 


Star's  decl. 

38 

41  6 

18 
90 

11  6 
00  00 

App.  mer.  alt. 
True  alt. 

71 
71 

48  54 
25  24 

2) 

il43 

14  18 

T.  alt.  71°  25' 24"      -4  56 
I.E.  +  5  20 

+  0'  24' 


Half-sum  alt.      71°  37'    9" 

Cosine  lat.,  by  D.R.  20°  30'   0"N.=  9.971591 
Cosine  decl.  38°  41'  6"      -=  9.89243  I  Logs,  corrected  to 

2  X  sine  H. A.  17'^  14«      =  7.15010  j  seconds. 

Secant  half-sum  alt.  71°  37'   9"     - 10.50124  I 


Sine        7.51536 
Nearest  7.50512     =11' 


Changeinj^^     3^.       3  1024     =^6' 

log.  for  1  \^^ 


Reduction, 

Star's  T.  alt.  71°  25  24    N. 


360 

I79 
180 


Z.D.     18    12  04    S. 
N. 
Change  for  l'  =  63)1024(16  Lat.     20°  29'  02"  S. 


11 

16 
2 

22 

32 

.  71° 

'  25 

24 

71 

47 

56 

90 

00 

00 

18 

12 

04 

38 

41 

06 

394 

378 


This  example  is  worked  to  seconds  throughout,  but  it  is  not 
necessary  in  practice. 

Example.— 1894:,  July  10th,  a.m.  at  ship,  in  lat.  29°  45'  N,  and 
long.  175°  45'  W.  by  D.R. ;  obs.  alt.  of  star  Fomalhaut,  when  out  of 
the  meridian,  30°  5'  30",  bearing  S.;  I.E.  —3'  20";  height  of  eye 
24  feet;  time  by  chronometer  July  lO-^  4:^  ^'^  25%  which  was  IB"" 
10^  fast  for  G.M.T.  Required  the  latitude  by  ex  meridian  alti- 
tude. 


Meridian  Altitude. 


99 


July  10"    4" 

7"' 

'25« 

Long. 

175°  45'    W. 

- 

13 

10 

4 

G.M.T.         10     3 

54 

15 

60)703 

-    11 

43 

00 

IP  43°^ 

S.M.T.                16 

11 

15 

Sid.  time,             7 

13 

35 

Table  3,  N.A. 

0 

38 

R.A.  of  mer.      23 

25 

28 

R.A.  of  star,      22 

51 

48 

Star's  hour-angle,    33™  40« 


Star's  decl.    30°  11'  02"S. 
Lat.  by  D.R.  29    45  00  N. 

59    56  02 
90    00  00 


Approx.  alt.  30    03  58 
T.  alt.  29    55  41 


2)59    59  39 
Half-sum,      29°  59'  49" 


Star's  obs.  alt.  30°    5'  30"   I.E.  3'  20" 
-      9  49     Dip,  4  48 

T.  alt.  29°  55'  41"   Ref.  1  41 
-9^" 


Cosine  lat.  29°  45'    0"  N.  =  9.93862 

Cosine  decl.         30    11     2    S.   =  9.93673 
2 X sine  H. A.  33™  40«        =7.73290 

Secant  half-sum,  29°  59'  49"        =10.06245 


Sine  7.67070=16' 
2 


Reduction, 


32' 


Star's  T.  alt. 

29°  55'  41" 
+  32 

S. 

30    27  41 

90    00  00 

Z.D. 

59    32   19 

N. 

Decl. 

30    11   02 

S. 

Lat. 

29°  21'  17" 

■N. 

DIVISION  V. 


LONGITUDE  BY  CHRONOMETER. 

The  Observation. — Station  an  officer  at  the  chronometer.  Take 
your  sextant,  bring  the  sun's  image  down  to  the  horizon,  and  then 
clamp  it;  call  to  the  officer  to  stand  by,  then  with  the  tangent- 
screw  make  the  lower  limb  of  the  sun  touch  the  horizon  very 
nicely,  and  immediately  call  out,  "Stop."  The  officer  will  then 
note  the  hours,  minutes,  and  seconds  shown  by  the  chronometer 
at  that  instant,  and  the  observer  will  read  the  sun's  obs.  alt.,  which 
must  be  marked  down  abreast  of  the  time  by  chronometer.  If  the 
horizon  be  not  very  well  defined,  take  four  or  five  sights,  and  get 
the  mean  of  them  by  adding  the  altitudes  together  and  dividing 
by  the  number  taken;  then  add  the  chronometer  times  together  and 
divide  by  the  same  number. 

Example. — Suppose  the  following  number  of  sights  were  taken 
when  the  horizon  was  not  very  clear. 


Alt.  18°  15' 

Chron.  time,     8'^  40"^ 

^  20« 

18    40 

8    41 

13 

18    42 

8    41 

18 

•18    52 

8    42 

10 

4)74    29 

4)34    45 

01 

:ean  of  obs.  alt.  18°  37' 

15" 

Mean 

of  chron.  time,  8''  41'" 

15« 

If  the  horizon  be  clear  and  the  sun  bo  seen  plainly,  one  sight  is 
as  good  as  a  dozen.  In  actual  sea  practice  the  error  of  the  chro- 
nometer is  known  for  every  day,  so  that  the  rating  is  required  only 
at  long  intervals. 

At  the  examination,  however,  the  candidate  will  be  required  to 
find  the  error  of  the  chronometer  given  in  the  question  to  find  the 
longitude. 


Longitude.  If^l 


EULE. 

To  Correct  the  Chronometer  Time.— To  the  time  by  chronome- 
ter apply  the  second  error,  adding  if  slow,  subtracting  if  fast.  Next, 
write  down  to  the  right,  under  each  other,  the  two  errors;  if  both 
should  be  slow  or  both  fast,  subtract,  or  if  one  be  fast  and  the 
other  slow,  add;  convert  the  sum,  or  remainder,  into  seconds  by 
multiplying  by  60,  and  divide  the  result  by  the  number  of  days 
between  the  dates  of  the  two  errors.  The  result  will  be  the  daily 
rate,  viz.,  what  the  chronometer  is  gaining  or  losing  in  one  day. 

To  Know  if  the  Daily  Bate  is  Losing  or  Gaining. 

From  fast   to  less    fast,    dnily  rate  is  losing. 
From  fast    to  more  fast,   daily  rate  is  gainin.. 
From  slow  to  more  slow,  daily  rate  is  losing. 
From  slow  to  less    slow,  daily  rate  is  gaining. 
From  slow  to  fast,  daily  rate  is  gaining. 

From  fast   to  slow,  daily  rate  is  losing. 

To  Find  the  Accumulated  Eate.—Y'md  the  number  of  days  and 
tenths  of  days  between  the  date  of  the  second  error  and  the  day  of 
chronometer  time  and  multiply  by  the  daily  rate,  crossing  off  from 
the  product  as  many  figures  as  there  are  decimals  contained  in  the 
question.  The  remainder  will  be  seconds,  and  is  called  the  accu- 
vnilaied  rate.  Convert  these  seconds  into  minutes  and  seconds 
if  more  than  GO.  Add  this  accumulated  rate  to  the  chronometer 
time  if  daily  rate  is  losing,  but  subtract  if  it  is  gaining.  The  re- 
sult will  be  the  correct  Greenwich  Mean  Time  (G.M.T.). 

To  Find  Tenths  of  Daijs.—^lavk  down  the  hours  and  tenths  of 
hours  of  the  chronometer  time  and  divide  by  24.  The  result  will 
be  tenths  of  a  day.  It  is  not  necessary  to  carry  it  to  more  than 
one  place  of  decimals. 

Correct  the  declination  for  G.M.T.,  the  same  as  it  is  done  in  Mer. 
alt.  and  amp.  problems. 

To  Find  the  Polar  Distance.— li  the  latitude  and  declination  are 
of  the  same  name,  subtract  the  declination  from  90°,  but  if  of 
different  names,  add  the  declination  to  90°.  The  result  in  either 
case  will  be  the  Polar  Distance  (P.D.). 


102  Taylor's  Modern  Xavigatiox. 


To  Correct  the  Equation  of  Time. — Take  from  page  2  of  the 
Nautical  Almanac  the  equation  of  time  for  the  Greenwich  day  and 
its  difference  for  one  hour.  Multiply  this  difference  for  one  hour 
by  the  hours  and  tenths  of  hours  of  the  G.M.T.,  and  cross  off  from 
the  product,  to  the  right,  as  many  figures  as  there  are  decimals  in 
the  question.  The  figures  that  are  left  will  be  seconds,  to  be  added 
to  the  Equation  if  it  is  increasing,  and  subtracted  if  it  is  decreas- 
ing. The  result  will  be  the  corrected  equation  of  time.  Take  the 
sign  of  addition  or  subtraction  to  or  from  apparent  time  from  the 
top  of  page  1  and  prefix  it  to  the  corrected  equation. 

Correct  the  sun's  obs.  alt.  as  usual  for  I.E.,  dip,  S.D.,  parlx., 
and  ref. 

The  Computation. — Mark  down  the  T.  Alt.,  Lat.,  and  P.D.  un- 
der one  another  and  add  them,  divide  the  sum  by  2  and  call  the 
result  the  half-sum,  subtract  the  T.  Alt.  from  the  half-sum,  and 
call  the  result  the  remainder. 

Take  out  of  Table  44  the  secant  of  the  latitude,  cosecant,  P.D., 
cosine  half-sum.  and  sine  of  the  remainder,  throw  away  the  index 
when  it  is  10,  add  these  four  logs.,  and  divide  the  sum  by  2.  This 
half-sum  is  the  sine  of  the  Apparent  Time  at  Ship  (A.T.S.), 
Table  44. 

Look  for  the  half-sum  in  the  sine  column,  and  if  it  cannot  be 
found  exactly,  take  the  next  less  log.  and  note  the  hours,  minutes, 
and  seconds  abreast  of  it  in  the  a.m.  column  if  it  is  a.m.  at  ship, 
but  in  the  p.m.  column  if  it  is  p.m.  at  ship ;  take  this  next  less  log. 
and  mark  it  down  under  the  half-sum  of  logs.,  subtract  them,  and 
look  in  the  little  table  at  the  bottom  of  the  page  for  the  difference 
abreast  of  A.  Take  the  nearest,  and  note  the  seconds  above  it;  add 
these  seconds  to  the  '^  ™  ®  if  it  is  v.^i.  at  ship,  and  subtract  if  a.m. 
at  ship.  The  result  will  be  the  civil  A.T.S.  If  it  is  a.m.  at  ship, 
add  12  to  the  hours  of  this  civil  time,  and  put  the  ship's  date  one 
day  back ;  if  p.m.  at  ship,  put  the  ship's  date  in  front  of  the  !>  ™  « 
The  result  in  both  cases  will  be  the  astronomical  apparent  time  at 
ship  (A.T.S.). 

Under  the  A.T.S.  put  the  correct  equation  of  time,  and  add  or 
subtract  it  according  to  the  instructions  on  top  of  the  equation 
column  on  page  1  of  the  Nautical  Almanac.  The  result  will  be 
the  mean  time  at  ship  (M.T.S.). 


LoXGnTDE.  103 


UiukT  the  M/r.S.  put  the  correct  G.M.T..  and  subtract  the  lesser 
from  the  greater.     The  remainder  will  be  the  longitude  in  time. 

Convert  this  longitude  in  time  into  longitude  by  multiplying 
by  GO  and  dividing  by  4. 

To  Name  the  Longitude. 

Greenwich  time  best    longitude  West. 

Greenwich  time  least  longitude  East.  . 

Example  for  Practice. 

Time  by  chronometer  :\Iarch  21^  20''  35"^  10%  which  was  4°^  20" 
fast  on  January  3d.  and  on  February  2d  was  7°^  5^  fast.  Required 
the  correct  G.M.T. 

March     21"  20"  35'"  10^  1st  error,  Jan.  3d,  4"'  2(>^  fast. 

-  7       .")  2d  error,  Feb.  2d,  7     05    fast. 


Approx.  21    20    28       5  2     45 

-  4     23  BO 


G.M.T.    21"  20''  23'"  42^  30)165(5^5  (daily  rate 

150  gaining.) 

150 
150 


From  Feb.  2d  to  end  of  month,  26  days.  20*'  28" 

Up  to  and  including  March  21st.  24) 20.5 (.8  (tenths  of 

5.5 


192  a  day.) 


2390 
2390 

60)262.90 

Accuni.  rate,  —4'"  23** 

It  will  be  noticed  that  the  second  error  is  subtracted  from  the 
chronometer  time  because  it  is  fast,  the  result  being  the  approxi- 
mate G.M.T. 

The  errors  are  subtracted  because  they  are  of  the  same  name, 
and  the  result  is  divided  by  the  number  of  days  between  the  two 
dates  to  obtain  the  dailv  rate,  gainins;  in  this  case  because  the  sec- 


104 


Taylor's  Modern  JSTavigatiox. 


ond  error  is  more  fast  than  the  first.  Next,  the  days  are  counted 
between  the  date  of  the  second  error  and  day  of  chronometer  time, 
and  the  tenths  are  also  fonnd;  these  days  and  tenths  are  multi- 
plied by  the  daily  rate.  The  result  is,  then,  the  accumulated  rate, 
to  be  subtracted  from  the  approximate  G.M.T.  because  daily  rate 
i.:-  gaining.     The  final  result  is  then  G.M.T. 

Example.— Time  by  chronometer  March  24*^  IS^^  56°^  10%  which 
was  fast  l""  29^  on  January  19th,  and  on  March  10th  was  2™  13^ 
slow.     Required  the  correct  G.M.T. 


March       24M5^56'"10« 
2d  error,  +   2     13*^ 

24  15  58    23 
Accum.rate,      +1      4 

G.M.T.,     24^5'^  59"^  27« 


1st  error,  Jan.      19th,  I'"  29«  fast. 
2d  error,  March  10th,  2     13    slow. 

Days,  50 


3     42 

60 


50)222(4^4  (daily  rate 
200  losing.) 

~^0 

Number  of  days  between  date  of  2d  error  

and  day  of  chronometer  time  is  14''.66      24)16'\0(.66  (decimals 
Daily  rate,        4.4  144  of  days.) 

leo 

144 


5864 
5864 

60)64.504 


1"^  4^=  accumulated  rate;  to  be 
added  to  the  chronometer  time  because  daily  rate  is  losing. 


In  this  case  we  must  add  the  second  error  to  the  chronometer 
time  because  it  is  slow;  and  as  one  error  is  fast  and  the  other  slow, 
we  must  add  them  and  bring  the  sum  into  seconds;  we  then  di- 
vide by  50,  the  number  of  days  between  the  errors;  as  50  will  go 
4  times  into  222,  4  is  a  whole  number;  we  then  borrow  a  cipher 
and  let  50  go  into  it  again  4  times;  this  is  a  decimal  because  we 
had  to  borrow  a  cipher  to  lot  50  go  into  it. 

In  finding  the  decimals  of  days  we  generally  put  down  the  hours 
and  tenths  of  hours  and  divide  by  24,  but,  in  this  case,  16  hours 
is  nearer  than  15  hours  and  nine  tenths,  therefore  we  divide  16 
hours  by  24  and  get  .(i(i;  we  then  multiply  the  days  and  decimals 


Longitude 


105 


of  days  between  the  2d  error  and  the  chronometer  time  by  the  daily 
rate,  and  as  we  have  three  decimals  in  the  question,  we  must  cut 
off  three  figures  from  the  product,  which,  in  this  case,  leaves  64 
seconds,  to  be  added  to  the  chronometer  time  because  daily  rate  is 
losing. 

Example. — Time  by  chronometer  November  11*^  1^  20™  5^  which 
on  April  30th  was  6'"  2^  fast  and  gaining  10^  daily.  Eequired  the 
correct  G.^^LT. 

Nov.  11"  1"  20'"    5«     April  00  (Nothing  in  April.) 
The  only  error,   -        6      2      May  31 

mnL4  3  j"!"^®  30 

Accum.rate,       -      32     30      J^^^  '^^     24)1\  20t(.05  (decimals 


Aug.  31 

G.M.T.  ll^OMl-33^     Sept.  30 

Oct.    31 
Nov.  11 


1  .20 


of  days.) 


195.05 
10. 

60)195.050 

32"^  30^  accum.  rate. 

As  2-1:  will  not  go  into  1.2,  we  borrow  a  cipher  and  put  this 
cipher  in  the  dividend;  then  it  wall  go  .05  times. 

In  this  case  we  have  only  one  error,  but  the  daily  rate  is  given, 
therefore  we  have  only  the  accumulated  rate.  The  number  of 
days  between  April  30th  and  November  11th  is  195.05,  which  mul- 
tiplied by  the  daily  rate  gives  32'"  30%  to  be  subtracted  from 
chronometer  time  because  daily  rate  is  gaining. 

Examples  in  Correcting  the  Equation  of  Time. 

Example.— March  21*^  201^  23"°  5G^  G.M.T.  Eequired  the  cor- 
rect equation  of  time. 


March  21st,  equa.  of  time,  =7"^  13^8 

Sub.  cor.,  because  equa.  is  decreasing,  —         15.5 


Correct  equa.  of  time, 


+  6'"  58^3 


106  Taylor's  Modern  Navigation. 

To  be  added,  because  it  says  so  on  the  top  of  the  column  on  page 
1,  Nautical  Almanac. 

Diff.  for  1  hour,     .759 
20.4 


3036 
15180 

15.4836 

As  there  are  four  decimal  figures  in  the  question,  we  must  cross 
off  four ;  but  take  the  first  one  and  apply  it  to  the  equation,  as  seen 
in  example. 

Exainple.— March.  24"*  lo^^  59™  27^  G.M.T.  Eequired  the  cor- 
rect equation  of  time. 

March  24th,  equa.  of  time  =6"^  18^82 

Equa.  is  decreasing  —       12  .28 

Correct  equa.  of  time  to  be  ^  lAm    aTTT 
added  to  app.  time             ) 

Diff.  for  1  hour         =.768 
16  hours  is  nearest  16. 


4608 

768 

12.288 


Example.— Becemhei  2^*^  lli^  20°^  50^  G.M.T.    Eequired  the  cor- 
rect equation  of  time. 

Dec.  24th,  equa.  of   time  =0'"  8\72  Diff.  1  hour=-   1".250 

-     14.12  1P.3 

Cor.  equa.,  to  be  added  }  ^^T^q  3750 

to  app.  time,  )  13750 


14.1250 


In  this  case  the  correction  is  greater  than  the  equation,  there- 
fore we  must  subtract  the  equation  from  the  correction;  and  the 
remainder  must  be  added  to  apparent  time  because  we  have  crossed 
the  black  lino.       (See  top  cohunn  in  Nautical  Almanac.) 


Longitude. 


107 


Example. — 'June  13*^ 
rect  equation  of  time. 


Vi"'  dS"  G.M.T.     Required    the    cor- 


June  13th,  equa.  of  time=0'"  12\00 

Decreasing,  —       12  .27 

Cor.  equa.,  to  be  added  )        ~ 

to  app.  time,  ^ 


Diff.  1  hour=     .51! 
23.7 


00«.27 


3626 
1554 
1036 

12.2766 


The  equation  is  decreasing,  therefore  we  must  subtract,  and  as 
the  correction  is  greater,  the  equation  must  be  subtracted  from  it. 
The  remainder  will  then  be  on  the  other  side  of  the  black  line,  and 
must  be  added  to  apparent  time.  (See  top  of  column  in  Nautical 
Almanac.) 

Example.— 1894,  May  2d,  p.m.  at  ship,  in  lat  31°  17'  N.;  the 
observed  altitude  of  the  sun's  L.L.  was  27°  1110";  I.E.  +4'  3"; 
height  of  eye  12  feet;  time  by  chronometer  May  1^  201^  57"^  20^ 
which  was  10""  6^  fast  on  March  17th,  and  on  April  1st  was  10°^  40« 
fast.    Required  the  longitude. 

May  1^20"  57'"  20nst  error,  Mar.  17th,  10'"  6^  fast. 
2d  error,  —    10    40  2d  error,  April  1st,  10    40  fast. 

Approx.        1  20   46 
Accum.  rate,     —      1 

30^9 


40 
11 


G.M.T. 


Id  20^  45'"  29« 

Daily  rate,  2.3 

"927 
618 


15)34(2^3  (daily  rate 
30  gaining.) 

45 


60)71.07 
Accum.  rate,     1"^  IV 


Decl. 


15°    9'31"N. 
+    15  36 

N. 


Diff.  1  hr. 
45.24 
20.7 


Cor.  decl.  15   25  07 
90   00  00 


24)20.8 (.9(tenths  of  days.) 
21.6 

Diff.lhr. 
3'"  2^77  0.305 
+  6  .31    20.7 

3'"  9^08        2135 
6100 

6.3135 


Equa. 


Sub. 
from  app.  T 


P.D. 


53"       60)936.448 
15'  36" 


108  Taylor's  Modern  Xavigation. 


] 
1 

..L.   27°  11'  10" 

-^•14  48 

[.E.         4'    3" 
^.D.      15  54 
^arlx.           8 

Obs.  alt.  I 

+  20  05 
-  5  17 

+  14' 48" 

True  alt. 

Lat. 

P.D. 

27    25  58 
31    17  00 
74    34  53 

sec       .06823 
cosec  .01591 

2)133    17   51 

Half-sum, 
T.  alt. 

66    38  55 
27    25  58 

cos     9.59808 

Remainder,      39°  12'  57" 

sine  9.80089 

Dip.,  3'  24' 
Ref.    1   53 

-5'  17' 


2)19.48311 

9.74155  sine  of  A.T.S. 
4h  27m  44s  p_M.   9.74151  next  less  log. 

2  4A=:2« 

May    2^    4    27     46    astronomical  A.T.S. 

Equa.  3       9    (to  be  sub.  from  apparent  time.) 

May     2      4    24     37    mean  time  ship. 
May     1    20    45     29    M.T.G. 

long,  in  time. 


Long.     114°         47'  00"  E. 

Xever  say  "miles  of  longitude":  it  is  not  correct;  say  "minutes." 
The  longitude  in  time  may  be  converted  into  longitude  by  Table 
7,  or  by  multiplying  the  hours  by  15  because  there  are  15°  in  one 
hour  of  time,  and  dividing  the  minutes  by  4  because  there  are  4 
minutes  in  a  degree  of  longitude,  and  the  seconds  by  4  because 
there  are  4  seconds  in  a  minute  of  longitude ;  thus : 

7''  39"^  08^ 
15 


2^    4    27 
3 

46 
9 

2     4    24 
1    20    45 

37 
29 

7    39 
60 

08 
180 

4)459 

188 

105     45     00  ■ 
9       2 

Long.  114°  47'     00" 


LONOITUDK 


109 


Exam  pic— ISdi,  December  5th,  A.M.  at  ship,  in  lat.  39°20'  N.; 
the  obs.  alt.  of  suivs  L.L.  was  7°  6'  00";  no  index  error;  height  of 
eye  24  feet ;  time  by  chronometer  December  5^  7^^  54™  3%  which  was 
S""  10**  fast  of  G.M.T.  Required  the  longitude  at  time  of  sight; 
and  supposing  the  ship  sailed  S.S.W.  true,  distance  36  miles,  from 
time  of  sight  to  noon,  what  is  the  position  of  ship  at  noon? 


Dec.  5*'  7^^  54'"    3^ 
Fast        -    9     10 


Diff.  1  hr. 
Decl.         22°  25'  18"  S.  18".74 

+  2  24  7.7 


Dec.  5'^  7''  44"'  53«  G.M.T.      Cor.  decl.  22    27  42    S.  13118 

90    00  00  13118 


Diff.  1  hr. 


Equa  9"'  8^76      1.045  P.D.  112°  27'  42"         60)144.298 

-       8.04      7.7  2' 24" 


Cor.  equa.  9"'  0^72   7315 
7315 

8.0465 


Obs.  alt.  L.L.     7°    6' 00" 
+  4   19 

True  alt.             7    10  19 
Lat.                   39    20  00 
P.D.                 112    27  42 

sec 
cose 

cos 
'  sin( 

+ 
S.  D.  16'  17" 
Parlx.           9 

+  16  26 
-12  07 

Dip,  4'  48' 
Ref.  7   19 

-12'  07' 

+  4'  19" 

.11156^ 
?c  .03428 

y    log. 
9.26131  j     ^^" 

3  9.97898. 

2)158    58  01 

Half-sum,         79    29  00 
T.  alt.                  7    10  19 

to  nearest 
utes^of  arc. 

Remainder,      72°  18'  41' 

2)19.38613 

Sine  9.69306 

Next  less  9.69301 


5A 


110  Taylor's  Moderx  Navigation. 


12^ 

0- 

■    2« 

8 

3 

36 

A.M. 

Dec. 

4'^20 

3 

34 

ast.  A.T.S. 

Equa 

.       - 

9 

1 

Dec. 

4    19 

54 

33 

M.T.S. 

Dec. 

5     7 

44 

53 

M.T.G. 

IP 

50« 

^  20^  long,  in  time. 

60 

120 

4)710 

140 

Long.  177°        35'  00"  W.  at  sight. 

T.  CO.  S.S.W.  36  =  D.  lat.  33'.3  S.;  dep.  13'.8  W. 
Position  of  ship  at  sight,  lat.  39°  20'  N.;  long.    177°  35'  W. 
D.  lat.  33  S.;  D.  long.         18  W. 

Position  of  ship  at  noon,  lat.  38°  47'  N.;   long.  177°  53'  W. 

Before  proceeding  any  further  with  the  chronometer  observa- 
tion, it  will  be  necessary  for  the  student  to  understand  that  the 
face  of  the  chronometer  has  only  12  hours  marked  on  it,  the  same 
as  any  ordinary  clock,  and  the  time  read  from  it  is  simply  civil 
Greenwich  mean  time. 

Therefore,  as  civil  time  is  reckoned  from  midnight  to  midnight, 
it  is  all-important  that  a  thorough  knowledge  of  handling  this 
time  be  possessed  by  the  navigator,  so  that  he  may  convert  the 
civil  into  astronomical  time  when  working  a  time  sight.  Ignorance 
of  this  subject  will  cause  the  navigator  to  make  a  very  large  error 
in  his  position ;  so  we  will  endeavor  to  explain. 

How  to  State  Astronomically  the  Time  Shown  by  a  Chronometer. 

If  the  observer  is  in  East  longitude,  his  time  is  always  ahead 
of  the  time  at  Greenwich  to  the  amount  of  his  longitude  in  time. 

If  in  West  longitude,  his  time  is  behind  Greenwich  to  the 
amount  of  his  longitude  in  time. 

If  it  is  A.M.  at  Greenwich  on  tbe  same  civil  date  as  at  ship,  add 
18  to  the  hours  shown  on  face  of  chronometer  and  place  the  ship's 
date  one  day  back. 

If  it  is  A.M.  at  Greenwich  on  next  civil  date,  add  12  to  the  hours 
and  keep  the  ship's  date. 

If  it  is  P.M.  at  Greenwich  on  same  civil  date  as  at  ship,  simply 
prefix  the  ship's  date  to  the  chronometer  time. 


Longitude.  Ill 


If  it  is  P.M.  at  Greenwich  on  the  day  before  ship's  civil  date, 
prefix  yesterday's  date  to  chronometer  time. 

In  either  of  the  above  cases  the  result  will  be  the  chronometer 
time  expressed  astronomically. 

To  Convert  Civil  Time  to  Astronomical  Time. 
The  astronomical  day  commences  at  noon  and  ends  the  follow- 
ing noon,  and  is  reckoned  from  0  to  24  hours. 

Example.— li  it  is  May  22d  at  2''  IG'"  00«  p.m.,  mark  the  date 
and  time  down  as  it  stands,  for  p.m.  civil  time  coincides  with 
astronomical  time,  but  if  it  is  May  22d  at  2'*  16"  00«  a.m.,  then  12 
must  be  added  to  the  hours,  and  the  date  placed  one  day  back,  to 
reckon  from  the  last  noon  that  has  passed.  The  reason  is  very 
obvious,  because  2"  16"^  00^  a.m.  is  the  time  from  midnight,  and 
midnight  is  12  hours  from  noon  of  the  preceding  day. 

Again,  supposing  it  to  be  lO'^  p.m.,  we  should  simply  call  it  10 
hours,  but  if  10''  a.m.,  we  must  call  it  22  hours  from  yesterday 
noon. 

It  it  be  l'^  A.M.,  it  would  be  13  hours;  if  2^'  a.m.,  14  hours;  if 
3"  A.M.,  15  hours;  if  2'*  p.m.,  only  2  hours;  if  3^  p.m.,  3  hours,  and 
so  on. 

^a;amj3Ze.— Supposing  we  looked  at  a  chronometer  when  it 
showed  8^  40"^  10^  when  the  date  at  ship  was  March  20th,  at  9^ 
A.M.  by  ship's  clock,  and  the  long,  by  D.K.  w^as  180°  W. 

Now,  180°  converted  into  time  equal  12  hours,  and  as  it  is  West, 
Greenwich  time  must  be  12  hours  ahead  of  ship's  time;  so  12  hours 
ahead  of  9^  a.m.  will  be  d^  p.m.  for  G.T.,  and  by  comparing  this 
with  the  chronometer  time  it  will,  no  doubt,  be  seen  that  the 
chronometer  is  showing  p.m.  at  Greenwich ;  therefore,  simply  place 
the  ship's  date  in  front  of  it ;  thus,  IMarch  20'^  8^  40»"  10%  astronomi- 
cal time  at  Greenwich. 

Same  Example. — Supposing  the  long,  to  be  East  instead  of 
West.  In  this  case  the  ship's  time  would  be  12  hours  ahead  of 
Greenwich  time;  therefore,  to  obtain  G.T.  we  must  go  back  12 
hours  from  ship's  time,  which  would  give  p.m.  of  yesterday  at 
Greenwich;  so,  place  yesterday's  date  in  front  of  the  chronometer 
time;  thus,  March  ig''  8»^  40"^  10«. 

Example.— July  10th,  at  about  10  o'clock  A.^^r.  at  ship,  a  chro- 
nometer showed  1^  42^"  40^  when  the  ship  was  in  long.  125°  E.  by 
D.E.     Ecquired  the   chronometer  time,   expressed   astronomically. 


112  Taylor's  Modern  Navigation. 


Long.  125°  E.=  8^  20"^  in  time;  as  it  is  East,  ship's  time  is 
ahead  of  Greenwich  time  that  amount;  so,  count  back  from  10  a.:m. 
8''  20°^,  and  we  shall  have  I''  40°*  a.m.,  and  by  comparing  this 
with  the  chronometer  time  it  will  be  noticed  that  the  chronome- 
ter is  showing  a.m.  at  Greenwich  on  the  same  civil  date ;  so,  to  con- 
vert this  civil  time  into  astronomical,  12  must  be  added  to  the 
hours,  and  the  date  placed  one  day  back.  The  answer,  then,  will 
be  July  9^  13^*  42"^  40^ 

Example. — July  20th,  p.m.  at  ship,  in  long.  150°  E.  by  D.K., 
a  chronometer  showed  6^  29°*  58^  Eequired  the  chronometer  time, 
expressed  astronomically. 

It  will  be  noticed,  in  this  example,  that  the  time  by  ship's  clock 
is  not  given,  but  it  is  easily  found,  as  will  be  seen. 

Long.  150°  E.  =:  10^  of  time,  and  as  it  is  East,  the  time  at  ship 
will  be  10^  ahead  of  what  the  chronometer  shows;  therefore,  count 
10^  ahead  from  chronometer  time,  and  we  have  4  p.m.  as  the  ap- 
proximate time  at  ship  at  the.  instant  of  looking  at  the  chronometer. 
Then,  if  it  was  4**  p.m.  at  ship,  and  this  time  is  lO*"  ahead  of 
chronometer  time,  it  is  very  apparent  to  the  student  that  the 
chronometer  is  showing  a.m.  at  Greenwich  on  the  same  civil  date 
as  at  ship ;  therefore,  add  12-  hours  to  the  hours  and  reckon  from 
yesterday's  date;  the  answer  will  then  be  July  19^  18^  29"^  58^ 

Example. — August  1st,  p.m.  at  ship,  in  long.  165°  W.  by  D.K., 
a  chronometer  showed  2''  17™  21^.  Required  the  chronometer  time, 
expressed  astronomically. 

Long.  165°  W.  =  ll"";  therefore  ship's  time  is  behind  G.T. 
11**;  count  back  from  the  chronometer  these  11  hours,  and  we  have 
3^  the  approximate  time  at  ship.  Now,  as  G.T.  is  ll""  ahead  of 
ship's  time,  it  will  be  noticed  that  chronometer  is  showing  a.m.  of 
next  civil  date  at  Greenwich,  therefore  12  must  be  added  to  the 
hours  and  the  date,  for  the  chronometer  time  will  be  the  same  as  the 
ship's. 

Answer.— August  1*^  14^  IT"*  21^ 

We  advise  the  navigator  to  learn  how  to  reason  the  time  out  as 
given,  but  in  case  of  his  not  being  able  to  do  so,  the  following  rule 
will  be  of  use,  providing  the  time  by  ship's  clock  is  known. 

If  it  is  a.m.  at  ship,  add  12  to  the  hours  shown  by  ship's  clock,  and 
put  ship's  date  one  day  back. 

If  p.m.  at  ship,  let  ship's  date  and  time  stand. 

In  either  case  the  result  will  be  the  approximate  astronomical 
time  at  ship. 


LONOITUDE.  113 


To  this  astronomical  time  at  ship  apply  the  long,  in  time,  adding 
if  West  lov.g..  subtracting  it  East  long.  The  result  will  be  the  ap- 
proximate astronomical  time  at  Greenwich.  Compare  the  astronomi- 
cal time  at  Greenwich  with  the  chronometer  time,  and  if  there  are 
more  than  12^  add  15''  to  the  chronometer  time,  but  if  less  than 
Iv^'',  let  the  chronometer  time  stand  as  it  is,  and  in  either  case  pre- 
fix to  the  chronometer  time  the  same  date  as  that  found  in  the  ap- 
proximate time. 

Example. 

June  14''  10''  a.m.  at  ship.  Long.  75°  E. 
12  ^     4 

13   22  60)300 

-    5E. 


June  13'^  17''  approx.  G.T. 


5"  0" 


Chron.  4''  54'^'  34« 
12 

June  13^  16"  54'"  34-^ 

Here  12  is  added  to  the  hours  because  approximate  time  is  more 
than  12. 

Examjjie. 

Aug.  18th,  9  A.M.  Long.  96°  W. 

12  4 


17  21  60)384 

+  6     24  \V. 


18"   3"   23'"  approx.  G.T. 

Ans.— Chron.  18**  3"  U""  45=^ 


6"  24' 


In  this  case  let  time  stand,  because  hours  in  approximate  time  are 
less  than  12. 

Examples  for  Practice. 

1.  June  3,      P.M.atship, inlong.ll5°W.,achron. showed  10"  57'"21" 

2.  Oct.  31,     P.M. 

3.  May  15,     a.m.        "        ' 

4.  Feb.  19,  8  a.m. 

5.  July  16,  4  P.M. 

6.  Oct.   23,     A.M. 

State  chronometer  time  astronomically. 

rAYt.OR's  Mod.   Nav.   S. 


179  W., 

3  19  14 

180  W., 

8  32  48 

53  W., 

11  21  40 

145  E., 

6  29  58 

135  E., 

0  6  41 

114  Taylor's  Modern  Navigation. 


Answers. 

Answers.— 1.  June  3^  lO'^  57"^  2V 

2.  Oct.  31,  15    19     14 

3.  May  15,  8    32     48 

4.  Feb.  18,  23    21     40 

5.  July  15,  18    29     58 

6.  Oct.  22,  12      6     41 

Example.— 1S94,  April  7th,  3^  34°^  p.m.  at  ship,  in  lat.  47°  54' 
N.;  long,  by  ace.  140°  W.;  alt.  of  sun's  L.L.  36°  40'  00";  a  chro- 
nometer showed  12'*  34™  50%  which  was  15'°  26«  fast  of  G.M.T.  on 
March  26th,  and  gaining  3^  daily ;  height  of  eye  20  feet.  Eequired 
the  longitude. 

April  7"  3'^    34'"  p.m.  Long.  140°  W. 

Long,  in  time,  +   9     20  4 

April  7^  12^*  54'"  approx.  G.T.  60)560 

9^  20°^ 

It  will  be  noticed  that  the  approximate  time  is  a  little  more  than 
12^  so  the  chronometer  must  be  the  same,  and  the  7th  day  is  pre- 
fixed, as  it  is  12**  34"  50^  from  noon  of  April  7th. 

April  7^  12'^  34'"  50«        Mar.  5'* 
Fast    -         15     26        April  7 

7    12    19     24  12.5 

—  38  3.    (daily  rate  gaining.) 

G.M.T.,  April  7''  12^  18'"  46^  37.5  (when  the  decimal  is  .5 

or  more,  increase  the 
whole  number  by  1.) 


Decl.         6°  55' 54"  N.  56".32  Equa.  2'"    6«.56  0^708 

+  11  33  12.3  -         8.70  12.3 

Cor. decl.  7   07  27   N.  16896  +P^57«.86  2124 

90   00  00  11264  1416 

P.D.        82°  52'  33"  ^^^^  _0708_ 


60)692.736  08^7084 

11'  33" 


Longitude. 

115 

+ 

_ 

S.D. 

16'  00" 

Dip,  4'  23" 

Parlx.           7 

Ref.  1   18 

+  16  07 

-5'  41" 

Obs.  alt.  L.L.  36°  40'  00" 

-  5  41 

+  10  26 

+  10'  26" 

T.  alt.               36    50  26 

Lat.                  47    54  00 

sec 

.17365 

P.D.                  82    52  33 

cosec 

.00336 

2)167    36  59 

Half-sum,        83    48  29 

cos 

9.03288 

T.  alt.               36    50  26 

Remainder,     46°  58'  03" 

sine 

9.86390 

2)19.07379 

sine        9.53689 
Nearest  9.53682 


Diff. 


'A  =  2« 


2* 

2^^ 

4im  4 

April 

7     2 

41     6   A.T.S. 

Cor.  equa. 

+ 

1  58 

7     2 

43  04   M.T.S. 

7  12 

18  46   M.T.G, 

9    35  42 
60     180 

4)575     222  120 
Long.  143°      55'    30"  W.  at  time  of  sight. 
Rule  to  Correct  a  Log.  Sine,  Tangent,  and  Secant  to  Seconds 

Take  the  difference  between  the  two  logs,  and  multiply  it  by  the 
seconds  and  divide  by  60.  The  result  will  be  the  correction,  to  be 
added  or  subtracted,  according  as  the  log.  is  increasing  or  decreas- 
ing. 

The  same  may  be  done  by  inspection,  thus : 

Search  under  S'  on  left-hand  side  of  page  until  the  required  num- 
ber of  seconds  is  found,  and  abreast  of  it,  in  the  difference  column, 
nearest  to  the  required  log.,  will  be  the  correction,  to  be  applied  to 
the  loff.  as  before. 


116  TAYLOifs  Modern  Xavigation. 


In  actual  practice  it  is  not  necessary  for  the  navigator  to  work 
logs,  to  seconds  of  arc. 

There  is  still  another  wrinkle  to  learn*  before  putting  the  longi- 
tude by  chronometer  problem  into  actual  practice,  which  the  fol- 
lowing explanation  will  enable  the  reader  to  understand: 

The  sight  to  obtain  the  longitude  must  be  worked  with  the  lati- 
tude the  ship  is  in  at  time  of  sight,  and  as  the  latitude  is  obtained 
at  noon  by  meridian  altitude,  or  near  noon  by  ex  meridian,  the  lati- 
tude at  those  times  must  be  reduced  to  observation  by  using  the  true 
course  and  distance  the  ship  has  sailed  between  sight  and  noon  when 
it  is  an  a.m.  sight,  and  from  noon  to  sight  when  p.m.  Work  back  the 
latitude  from  noon  when  it  is  a.m.^  and  work  ahead  from  noon  when 
P.M.,  and  the  longitude  found  in  both  cases  by  using  the  reduced 
latitude  will  be  the  longitude  of  ship  at  time  of  sight. 

Bring  this  longitude  forward  from  sight  to  noon,  if  it  is  A.M.,  by 
using  the  diff.  of  long.,  and  work  back  the  long,  to  noon  if  it  is  P.M., 
and  the  result  in  either  case  will  be  longitude  of  ship  at  noon. 

Example. — Take  a  sight  to  find  long,  as  usual,  and  note  the  true 
course  and  distance  the  ship  gailed  between  the  time  of  observation 
and  noon.  Enter  Table  2  with  the  true  course  and  distance  and 
take  out  the  diff.  of  lat.  and  dep.  and  mark  them  down. 

To  Find  the  Correct  Latitude  to  Work  the  Sight. — If  it  is  an  a.m. 
sight,  reverse  the  name  of  the  D.  lat.  made  good,  and  work  the  noon 
lat.  back  to  sights. 

Example. — Suppose  the  true  course  and  distance  from  an  a.m. 
sight  to  noon  was  JST.XE.  27  miles,  and  the  lat.  by  observation  at 
noon  was  46°  50'  N.  Required  the  latitude  of  the  ship  at  the  time 
of  sight. 

Course  N.XE.  27=D.  lat.  26.5;  dep.  5.3. 

Lat.  at  noon,  46°  50'    N. 

Diff.  of  lat.  26^    S.  (opposite  of  N.) 

Lat.  at  sight,  46°  23^  N. 

Tlie  course  the  ship  actually  steered  was  X.XE.  true,  but  we 
must  reckon  the  diff'.  of  lat.  South,  because  we  are  working  hack- 
wards  from  the  noon  lat.  to  obtain  the  lat.  of  the  ship  at  time  the 
sight  was  taken.  In  this  case  the  proper  lat.  to  work  the  sight 
would  be  46°  23'  30"  N. 


LoXGITUnE.  11' 


After  working  the  sight  and  obtaining  the  long.,  bring  it  for- 
vrard  to  noon  by  the  diff.  of  long,  the  ship  has  made  since  the  sight 
was  taken.  In  this  example  the  dep.  is  5.3,  which  is  equal  to  8'  of 
long.,  and  must  be  applied  to  the  eastward  of  the  long,  at  sight, 
because  the  ship  sailed  East  since  the  sight  was  taken. 

To  Find  the  Correct  Latitude  to  Work  a  P.M.  Sight.— Bv'mg  the 
lat.  found  at  noon  forward  to  the  time  of  sight,  by  the  true  course 
and  distance  the  ship  has  sailed  since  noon. 

Enter  Table  2  with  the  true  course  and  distance  as  before,  and 
take  out  the  diff.  of  lat.  and  dep.  Apply  the  diff.  of  lat.  to  the  noon 
lat.  in  the  ordinary  way,  and  you  will  have  the  correct  lat.  to  work 
a  P.M.  sight.  After  w^orking  the  sight  and  finding  the  long.,  work 
it  back  to  noon,  by  applying  the  diff.  of  long,  the  ship  has  made 
since  noon  in  the  opposite  direction  to  what  she  made  it;  that  is, 
if  the  ship  sailed  East,  allow  it  to  the  West  of  the  long,  at  sight,  and 
if  West,  allow  it  to  the  P]ast,  to  obtain  the  long,  of  the  ship  at  noon. 

Example. — Supposing  it  is  a  p.m.  sight,  and  the  true  course  and 
distance  between  noon  and  sight  was  S.  69°  W.  49  miles,  the  lat.  by 
observation  at  noon  being  38°  10'  S.  Find  the  latitude  to  work 
sight. 

T.  CO.  S.  69^  W.  49=D.  lat.  17.6;  dep.  45.7. 

Lat.  at  noon,  88°  10'  00"  S. 

D.  lat.  17  36    S.  (6X6=36) 

Lat.  at  sight,  38°  27'  36"  S.  (working  ahead.) 

And  supposing  the  long,  at  sight  to  be  116°  17'  W.,  what  is  the 
long,  at  noon? 

Long,  at  sight,  116°  17'  W. 

Dep.  45.7  =  diff.  of  long.  58  (working  back.) 

Long,  at  noon,  115°  19'  W. 

Example. — Supposing  it  is  an  a.m.  siglit,  true  course  S.  73°  W., 
distance  39  miles;  lat.  at  noon  29°  37'  S.     Find  latitude  at  sight. 
T.  CO.  S.  72°  W.  39=D.  lat.  12.1;  dep.  37.1. 

Lat.  at  noon,  29°  37'  00"  S. 

D.  lat.  12     6    N.  (worked  back.) 


Lat.  at  sight.  29°  24'  54"  S. 


118  Taylors  Modern  IS^avigation. 


And  supposing,  also,  that  the  long,  at  sight  is  172°  22'  E.     Find 
long,  of  ship  at  noon. 


Long,  at  sight,  172°  22'    E. 

Dep.  37.1  =  D.  long.  42^   W.  (worked  ahead.) 

Long.  171°  39i'  E.  at  noon. 


Example. — 1894,  November  llth,  a.m.  at  ship ;  obs.  alt.  of  sun's 
L.L.  was  21°  28'  00";  height  of  eye  10  feet;  time  by  chronometer 
IC*  42"  28%  which  was  42™  23''  slow  for  G.M.T. ;  lat.  of  ship  at 
noon  47°  08'  S.;  compass  course  between  sight  and  noon  N.  46° 
W.,  distance  45  miles;  deviation  7°  E.;  variation  by  chart  5°  E.; 
approximate  long,  at  time  of  sight  108°  E.  by  D.E.  Required  the 
position  of  ship  at  noon. 


Nov.  11*^    8^^  a.m.  (the  10th  day  must  be  prefixed  Long.  108 

12             to  the  chronometer  time  because  4 

10   20            it  is  showing  p.m.  of  yesterda}'  60)432 

_     Y    12m  at  Greenwich.) 


7^  12^ 


10<^  12^^  48" 


Chron.  Nov.  lO"^  10'^  42--  28^  Decl.  17°  14'  09"  S.         41".97 

+    42     23  +7  58  11.4 


G.M.T.  lO-i  IP  24""  5P 

17    22  07 

16788 

90    00  00 

4197 

P.D. 

72°  37'  53" 

4197 
60)478.458 

7'  58' 

Equa.            15"^^  56^54 

0.257 

-02  .92 

11.4 
1028 

Cor.  equa. -15'"  53\62 

0257 

0257 

02^9298 


Longitude. 

119 

Obs.  alt.  21°  28'  00" 
+  10  47 

+ 
S.D    16'  12"                   Dip, 
Parlx.         8                     Ref. 

8'  06" 

2  27 

T.  alt. 

21°  38'  47" 

+  16  20 
-  5  33 

-5'  33" 

+  10' 47" 

Comp. 
Dev. 

CO.  N.  46°  W. 
7    E. 

Lat.  at  noon,          47°  08' 
D.  lat.                             37 

00"  S. 

18    S. 

Mag. 
Var. 

N.  39    W. 
5    E. 

Lat.  to  work  sight,  47°  45' 

18"  S. 

T.  CO. 

N.  34°  W.  45  = 

D.  lat.  37.3;  Dep.  25.2. 

T.  alt.        21' 
Lat.            47 
P.D.           72 

=  38' 
45 
37 

'47" 
18     sec         .17243 
53     cosec     .02026 

2)142 

01 

58 

Half-sum,71 
T.  alt.        21 

00 

38 

59     cos       9.51227 
47 

49' 

=  22' 

'  12"  sine     9.88020 

2)19.58516 

sine     9.79258 
79256 

2A  =  P 

12" 
6 

53 

20 

Nov.     10M8 
Equa.             — 

53 

15 

19  A.T.S. 
54 

10    18 
10    11 

37 
24 

25  M.T.S. 
51  M.T.G. 

7'^ 
60 

12'" 

34« 

4)432 

34   120 

Long,  at  sight,  108 
D,  long. 

8     30    E. 
38     00    W. 

Long,  at  noon,  107*^ 

) 

30'    30"  E. 

120 


Taylor's  Modekx  Xavigatiox. 


Example.— 18\) 4:.  August  21st.  o  p.m.  at  ship,  the  obs.  alt.  o\ 
sun's  L.L.  was  2.2°  14'  41";  dip  36  feet;  time  by  chronometer 
IQh  4^m  55s^  which  was  fast  16™  9^  for  G.M.T. ;  lat.  of  ship  at  noon, 
by  observation,  47°  23'  IST. ;  course  by  compass  between  noon  and 
sight  S.  36°  W.,  distance  47  miles;  deviation  3°  W.;  variation 
10°  E.;  approximate  long.  86°  W.  by  D.R.  Required  the  position 
of  ship  at  noon. 


Aug.      2V'  10'^  47" 
Fast                    10 

'  55^* 
09 

Decl.  12°     2'  51" 
-       8  46 

N. 

50".09 
10.5 

G.M.T.  21^'  10'^  31" 

^  46'' 

Cor.  decl.  11    54  05 
90    00  00 

P.D.  78°  05'  55" 

25045 
50090 

60)525.945 

8' 46' 


Equa. 

Cor.  equa.  +2™  51 


2"^  58^23 
-  06  .44 


0.614 
10.5 

3070 
06140 

06».4470 


Comp.  CO.  S.  36°  W. 
Dev.  3    \V. 


Lat.  at  noon,  47°  23'  00"  N. 
D.  lat.  34   24      S. 


Lat.  at  sight,  46°  48'  36"  N. 


Mag  CO.      S.  33    W. 
Var.  10     E. 

T.  CO.  S.  43°  W.  47  =  D.  lat.  34.4;  dep.  32.1  =  D.  long.  47'. 


Obs.  alt.  22°  14'  41" 
+  7  45 


T.  alt.      22°  22'  26" 


+ 

— 

S.D.  15'  51" 

Dip,  5'  53' 

Parlx.           8 

Ref.    2  21 

+  15  59 

-8'  14' 

-  8   14 

+   7' 45' 


LOXGITUDE.  121 


T.  alt. 

22°  22'  26" 

Lat. 

46    48  36 

sec 

.16468 

P.D. 

78    05  55 

cosec 

.00944 

2)147    16  57 

78    38  28 

cos 

9.44972 

22    22  26 

sine 

51°  16' 02" 

9.89213 

2)19.51597 

9.75798 


5« 
'  28 

Next  less,  9.75787 

4h  39,.: 

11 

21    4    39 

+   2 

33 

52 

A.T.S. 

21    4    42 
21  10    31 

25 
46 

M.T.S. 
M.T.G. 

11A=5« 


5    49     21 
60  60 

4)349  81 


Long.        87  20    15    W.  at  sight. 

47    00    E.  (worked  back.) 

Long.        86°         33'  15"  W.  at  noon. 

Examples  for  rractice. 

1894,  January  7th,  p.m.  at  ship,  in  lat.  5°  21'  N. ;  long,  by  ace. 
163°  E. ;  obs.  alt.  of  sun's  L.L.  17°  20'  00" ;  I.E.  —1'  2" ;  eye  21  ft. ; 
time  by  chron.  5^  48'°  39^  which  on  November  22d  was  G'"  10^  fast 
and  on  December  25th  was  4™  5^  fast.  Eequired  the  longitude  by 
chronometer. 

Answer. — Daily  rate  3^8,  losing;  accum.  rate  48^;  G.M.T.  Jan- 
uary 6^  17''  45"^  22-^;  cor.  decl.  22°  22'  42"  S.;  P.D.  112°  22'  42"; 
cor.  equa.  -ffi"'  29M5;  T.  alt.  17°  27'  49";  sum  of  logs.  19.50203; 
S.A.T.  7*5  4»'  34'"  29«;  M.T.S.  7'^  4^'  40'"  58^  long.  163*  54'  E. 

1894,  March  3d,  4"  36'"  p.m.  at  ship,  in  lat.  31°  14'  N.;  long,  by 
ace.  174°  W.;  obs.  alt.  of  sun's  L.L.  16°  49'  00";  I.E.  +3'  40"; 
eye  17  ft.;  time  by  chron.  4^  12""  10%  which  was  fast  2"^  10^  on 
January  21st,  and  on  March  1st  was  2"^  40^  slow.  Eequired  the 
longitude  by  chronometer. 


122  Taylor's  Modern  Xavigatiox. 


Answer. — Daily  rate  7^4,  losing;  accum.  rate  20^;  G.M.T.  March 
3'i  IG^  IS'"  10«;  cor.  decl.  6°  27'  02"  S.;  cor.  equa.  +11°^  54^59; 
T.  alt.  17°  01'  46";  sum  of  logs.  19.46761;  S.A.T.  2^  4"^  22"^  25^ 
M.T.S.  S^  4:^  34'"  20«;  long.  175°  12'  30"  W. 

1894,  March  20th,  8"  25""  a.m.  at  ship,  in  lat.  21°  38'  N. ;  long, 
by  ace.  156°  W.;  obs.  alt.  of  sun's  L.L.  31°  23'  10";  I.E.  —0'  20"; 
eye  36  ft.;  time  by  cnron.  6^  48™  46®,  which  had  been  found  to  be 
fast  O""  26«  on  January  20th,  and  on  February  27th  it  was  0"^  3^ 
slow.     Eequired  the  longitude  by  chronometer. 

Answer. — Daily  rate  .8%  losing;  accum.  rate  17^;  G.M.T.  March 
2od  Qh  49m  gs.  cor.  decl.  0°  3'  53"  IST.;  cor.  equa.  +7'°  26^84;  T.  alt. 
31°  31'  26";  sum  of  logs.  19.34028;  A.T.S.  191  20"  16-"  49®;  M.T.S. 
19<^  201^  24'"  16®;  long.  156°  12'  30"  W. 

1894,  April  14th,  p.m.  at  ship,  in  lat.  48°  21'  N.;  long,  by  ace. 
170°  W.;  obs.  alt.  of  sun's  L.L.  29°  59'  00";  I.E.  —00'  00";  eye 
30  ft. ;  time  by  chron.  2^  58'"  43®,  which  on  December  25,  1893,  was 
6"^  30®  fast,  and  losing  1®.9  daily.  Required  the  longitude  by 
chronometer. 

Answer.— Daily  rate  3""  30®;  G.M.T.  April  14^  14''  55"'  43®;  cor. 
decl.  9°  43'  44"  N.;  cor.  equa.  +0"'  4^33;  T.  alt.  30°  08'  00";  sum 
of  logs.  19.32850;  A.T.S.  14"^  3"  39"'  55®;  M.T.S.  14*  S''  39"'  59®; 
long.  168°  55'  W. 

1894,  June  4th,  at  7"  30-"  a.m.  at  ship,  in  lat.  17°  20'  N. ;  obs.  alt. 
of  sun's  U.L.  31°  10'  10";  I.E.  —1'  2";  eye  20  ft.;  time  by  chron. 
June  3*^  22*'  40"*  15®,  which  was  fast  5"*  10®  on  February  1st,  and 
on  April  10th  was  0""  10®  slow.  Required  the  longitude  by  chro- 
nometer. 

Answer. — Daily  rate  4®.7,  losing;  accum.  rate  4™  18®;  G.M.T. 
June  3**  22"  44"'  43®;  cor.  decl.  22°  27'  46"  N.;  cor.  equa..  — 1"" 
56®.04;  T.  alt.  30°  47'  20";  sum  of  logs.  19.43822;  A.T.S.  3^  19" 
47"'  20®;  M.T.S.  3'^  19"  45'"  24®;  long.  44°  50'  15"  W. 

1894,  August  10th,  10  o'clock  a.m.  at  ship,  in  lat.  46°  31'  S.; 
long,  by  ace.  135°  W.;  obs.  alt.  of  sun's  L.L.  18°  20'  30";  I.E.  + 
4'  15" ;  eye  16  ft. ;  time  by  chron.  7"  18"'  40®,  which  was  slow  3"'  4® 
on  March  11th,  and  losing  0®.7  daily.  Required  the  kmgitude  by 
chronometer. 

Answer.— Accum.  rate  1"'  47%  losing;  GM.T.  August  lO'*  7"  23"' 
31®;  cor.  decl.  15°  24'  59"  N.;  cor  equa.  +5"'  7^48 ;  T.  alt.  18°  34' 
3";  .sum  of  logs.  19.05930;  A.T.S.  9''  21"  21"'  41®;  M.T.S. 
9^  21"  26"'  48®;  long.  149°  10'  45"  W. 


Longitude.  123 


1894,  September  24th,  p.m.  at  chip,  in  lat.  38°  02'  S.;  long,  by 
aec.  120°  10'  E.;  obs.  alt.  of  sun's  U.L.  11°  34'  40";  I.E.  +10'  5"; 
eye  12  ft. ;  time  by  ehron.  September  23'^  18^  20°»  5%  which  was  1" 
3"  slow  on  January  20th  and  on  August  1st  was  11™  43^  slow.  Ee- 
quired  the  longitude  by  chronometer 

Answer. — Daily  rate  3^3,  losing;  accum.  rate  2™  57*;  G.M.T. 
September  23^  18'»  34°^  45*;  cor.  decl.  0°  28'  16"  S.;  cor.  equa. 
— T°»  57*.94;  T.  alt.  11°  20'  47";  sum  of  logs.  19.57791;  A.T.S. 
24<i  5b  3m  4p.  M.T.S.     24*^  4^  oo""  43*;  long.  155°  14'  30"  E. 

1894,  July  24th,  p.m.  at  ship;  lat.  of  ship  at  noon  46°  10'  S.; 
obs.  alt.  of  sun's  L.L.  18°  38'  30";  I.E.  +7'  00";  eye  30  ft.;  time 
by  chron.  10^  15™  32*,  which  on  February  7th  was  38"°  42*  fast  for 
G.M.T.,  and  on  May  16th  was  35'"  16*.2  fast  for  G.M.T. ;  compass 
course  between  sight  and  noon  S.  18°  E.,  dist.  39  miles;  var.  5° 
W. ;  dev.  3°  W. ;  long,  of  ship,  by  D.E.,  West.  Required  the  longi- 
tude of  ship  at  noon. 

Answer.— G.M.T.  24''  9^  42°^  42*;  P.D.  109°  44'  58";  T.  alt. 
18°  53'  12";  lat.  at  sight  46°  45'  06"  S.;  equa.  +6'"  17*;  half-sum 
of  logs.  9.38238;  A.T.S.  24<'  OP  51°^  40*;  long,  at  sight  116°  11' 
15"  W.;  long,  at  noon  116°  36'  15"  W. 

1894,  June  24th,  a.m.  at  ship;  lat.  of  ship  at  noon  54°  20'  12" 
N.;  obs.  alt.  sun's  L.L.  36°  43'  15";  I.E.  +3'  00";  eye  30  ft.; 
time  by  chron.  2*^  14°*  8%  which  on  April  2d  was  7™  14*.7  fast  for 
G.M.T.,  and  losing  4-''.9  daily  for  G.M.T. ;  course  by  compass  be- 
tween sight  and  noon  N.  74°  E.,  dist.  49  miles;  var.  17°  E. ;  dev. 
9°  W. ;  long,  of  ship,  by  D.E.,  West.  Ecquired  the  longitude  of 
ship  at  noon. 

Answer.— G.M.T.  June  24'^  2^'  13°^  40*;  P.D.  66°  34'  43"; 
equa.  +2"^  10*;  T.  alt.  36°  55'  28";  lat.  at  sight  54°  13'  24"  X.; 
A.T.S.  23"  20^  4™  59*;  long,  at  sight  91°  37'  45"  W.;  long,  at  noon 
90°  15'  15"  W. 

1894,  March  4t]i.A.M.  at  ship;  lat.  of  ship  at  noon  39°  57'  X. ;  obs. 
alt.  sun's  L.L.  17°  28'  30";  I.E.  —3'  00";  eye  30  ft.;  time  by 
chron.  1*^  4™  51%  which  on  December  8th  was  56""  38*  slow  for 
G.M.T.,  and  gaining  1*.4  daily  for  G.M.T. ;  course  by  compass  be- 
tween sight  and  noon  S.  48°  E.,  dist.  43  miles;  var.  6°  E.;  dev. 
6°  E. ;  long,  of  ship,  by  D.R.,  East.  Eequired  the  longitude  of  ship 
at  noon. 

Answer.— G.:\I.T.  :\Iarch  3'^  13'>  59'"  29*;  P.D.  96°  29'  20"; 
equa.  +11™  56*;  T.  alt.  17°  33'  24";  lat.  at  sight  40°  31'  48"  X.; 
A.T.S.  3^  19'^  59™  8*;  long,  at  noon  93°  26'  45"  E. 


I'^i  Taylor's  Moderx  Xavigation. 

1894,  December  23d,  p.m.  at  ship;  lat.  of  ship  at  noon  47°  26'  S. ; 
obs.  alt.  sun's  L.L.  26°  48'  00"  ;  I.E.  —6';  eye  28  ft. ;  time  by  chron. 
S""  lO'"  6%  which  on  July  21st  was  slow  6"°  13*  for  G.M.T.,  and  on 
Xovember  3d  was  4""  49**  slow  for  G.M.T. ;  compass  course  between 
sight  and  noon  X.  28°  W.,  dist.  44  miles;  var.  16°  W.;  dev.  12° 
E. ;  long,  of  shij).  by  D.L*.,  East.  Required  the  longitude  of  ship  at 
noon. 

Answer.— G.M.T.  December  22"^  20''  14°*  15«;  P.D.  66°  33'  13"; 
cqua.  — 0-"  43■^;  T.  alt.  26°  51'  20";  A.T.S.  231  gh  Qm  20^;  long,  at 
noon  131°  54'  30"  E. 

THE  MODERX  METHOD  OF  WORKIXG  AX  A.M.  SIGHT. 

The  preceding  rules  anent  the  finding  of  the  longitude  by  chro- 
nometer are  all  very  well  in  their  places,  but  they  involve  tedious 
waiting  for  the  noon  latitude,  and  consequent  delay  in  ascertaining 
the  ship's  longitude  at  both  time  of  sight  and  noon.  The  following, 
we  hope,  will  be  of  use  in  the  actual  practice  of  navigation, — in  fact, 
the  rule  is,  and  has  been  for  a  number  of  years,  in  use  on  large 
ocean  liners,  and  has  been  used  by  the  writer  daily  when  at  sea. 

It  will  be  noticed,  when  working  the  previous  method,  that  the 
observer  must  wait  until  noon  to  obtain  the  latitude,  and  that  this 
latitude  must  be  reduced  backwards  to  time  of  sight  before  it  is 
possible  to  work  it  out  to  obtain  the  longitude  at  time  of  sight ;  then 
this  longitude  must  be  brought  forward  to  noon  by  D.R.,  as  before 
explained,  to  obtain  the  ship's  position  at  noon,  involving  consider- 
able delay  after  the  noon  observation  before  place  of  ship  is  deter- 
mined, specially  if  the  navigator  is  a  little  slow,  causing  consider- 
able comment  among  the  wise  ones  of  the  ship's  company. 

It  is  not  necessary  to  wait  until  noon  before  working  the  sight, 
as  will  be  seen  by  perusing  the  following  very  carefully. 

As  soon  as  the  sight  is  taken  in  the  morning,  work  it  out,  using 
the  latitude  by  D.R.  The  result  will  be  the  approximate  position  at 
time  of  sight. 

Xcxt  enter  the  Sun's  True  Bearing  or  Azimuth  Tables  with  the 
A.T.S. ,  Latitude,  and  Declination  contained  in  the  sight,  and  take 
out  the  Sun's  True  Bearing  or  Azimuth,  which  must  be  always 
reckoned  less  than  90°.  being  careful  to  give  it  the  proper  name, 
according  to  tlic  instructions  on  bottom  of  each  page  of  the  tables; 
subtract  this  True  Azimuth  from  90°,  and  name  the  result  the  Co- 
J I  oaring. 


LON'GITUDE.  12.; 


The  navigator  has  all  the  forenoon  to  do  this  work,  which  is  a 
great  boon  to  slow  men. 

Xow.  a  few  minutes  before  noon,  let  us  say  about  fifteen  minutes, 
bring  the  approximate  position  at  time  of  sight  ahead  to  noon  by 
using  the  True  Course  and  Distance  the  ship  has  sailed  in  the  in- 
terval. This  will  give  an  approximate  position  at  noon,  but  will 
not  be  the  correct  one  unless  the  correct  latitude  was  used  to  work 
the  sight ;  but  read  on  a  little  further. 

Xext  correct  the  sun's  declination  for  the  approximate  longitude 
for  noon,  and  we  are  all  ready  to  take  the  noon  sight  to  obtain  the 
latitude. 

Eemember.  all  this  work  is  done  before  noon. 

Xow  take  the  noon  sight  and  obtain  the  latitude,  and  if  it  does 
not  correspond  with  the  approximate  latitude  brought  forward,  then 
the  approximate  longitude  is  not  correct,  but  we  may  correct  it, 
without  working  it  all  over  again,  by  the  following  rule: 

Eule  to  Correct  tJie  Longitude  for  an  Error  in  tlie  Latitude. 

Turn  up  Table  2  in  Bowditch  Epitome  and  enter  it  with  the  Co- 
bearing  as  a  course;  look  in  the  latitude  column  for  the  difference 
between  the  correct  latitude  at  noon  and  the  approximate  one;  when 
found,  note  the  dep.  abreast  of  it,  convert  this  dep.  into  diff.  of  long, 
by  the  rule  used  in  the  day's  work,  and  the  result  will  be  the  cor- 
rection, to  be  applied  to  the  approximate  longitude  at  noon  to  ob- 
tain the  correct  longitude  at  noon. 

Eule  to  Apply  the  Correction. — Mark  down  the  name  of  the 
Sun's  True  Azimuth,  and  under  it  the  opposite,  then  that  letter 
which  is  diagonally  opposed  to  the  name  of  the  correction  for  the 
latitude  will  be  the  name  of  the  correction  for  the  longitude;  thus 
supposing  the  name  of  the  Azimuth  to  be  X.E., 
under  it  mark  S.W., 
and  supposing  the  correct  latitude  is  to  the  Xorth  of  the  approxi- 
mate one.  then  place  the  pencil  on  X.  and  draw  a  line  to  W.,  and 
\V.  will  be  the  name  of  the  correction. 

This  method  of  working  may  be  still  further  improved  by  work- 
ing the  probhni  of  latitude  by  ex  meridian  altitude  about  five  min- 
utes before  noon,  anticipating  the  meridian  altitude ;  then  leaving  an 
officer  to  take  the  meridian  altitude  as  a  check,  it  is  possible  to  ob- 
tain the  ship's  position  before  the  last  tap  is  out  of  the  bell  at  noon. 


I'iij  Taylor's  Modern  Navigation. 

We  confidently  expect  that  these  rules  will  be  of  great  benefit 
to  the  modern  navigator,  and  he  is  requested  to  j^rove  them  for  him- 
self, by  working  a  few  sights  by  the  old-fashioned  method  as  a  test. 
We  do  not  expect  the  old  Xoahs  to  try,  as  it  is  hard  to  teach  an  old 
sea-dog  new  tricks. 

This  modern  method  of  working  the  sight  may  be  plotted  on  a 
chart,  provided  it  is  of  a  sufficiently  large  scale. 

After  working  the  observation  and  obtaining  the  approximate 
position  of  the  ship  and  also  the  Sun's  Azimuth,  proceed  as  follows: 

Mark  down  on  the  chart  the  approximate  latitude  and  longitude 
the  ship  is  in  at  time  of  sight,  draw  a  line  through  this  position  at 


a  right  angle  (90°)  to  the  Sun's  True  Bearing;  the  result  will  give 
a  line  of  position,  and  the  ship  i«  somewhere  on  this  line  at  time  of 
observation.  From  anywhere  on  this  line  lay  off  the  true  course 
and  distance  the  ship  sailed  between  sight  and  noon,  and  draw 
another  line  through  the  end  of  the  course  and  distance  line, 
parallel  to  the  first  line  of  position,  and  call  this  last  one  the  pro- 
jected line ;  the  ship  is  now  somewhere  on  this  line  at  noon.  Xext 
lay  down  the  latitude  the  ship  is  in  at  noon  and  draw  a  line  through 
it  until  it  crosses  the  projected  line,  and  the  point  where  the  pro- 
jected line  cuts  the  latitude  line  will  be  the  ship's  position  at  noon. 
The  above  is  simply  half  a  Sumner's  Method  worked  with  a  com- 
mon meridian  altitude  problem. 


LoxGiTroK.  127 


A  P.M.  sight  may  be  worked  by  this  method  also.  Thus,  suppos- 
ing a  sight  was  taken  about  four  o'clock  in  the  afternoon,  and 
worked  up  with  the  latitude  by  D.E.  as  before,  and  supposing,  also, 
that  the  correct  latitude  was  ascertained  by  observing  a  fixed  star 
or  planet  about  nine  p.m.,  then  the  latitude  and  longitude  being 
brouglit  forward  as  before,  and  the  latitudes  not  corresponding,  the 
longitude  may  be  corrected  for  the  error  in  the  latitude  and  ship's 
position  correctly  determined  at  nine  p.m. 

Example. — 1894,  February  12th,  10''  40"^,  a.m.,  when  ship  was  in 
lat.  38°  00'  N".  and  long.  160°  E.  by  D.R.,  the  following  sight  was 
taken  to  ascertain  the  longitude,  and  worked  up  immediately: 
Chron.  12'^  35'"  00^  which  was  ll"*  26"  fast  of  G.M.T.;  obs.  alt.  of 
sun's  L.L.  35°  43'  00" ;  height  of  eye  26  feet.  True  course  of  ship 
from  sight  to  noon  X.  28°  W.,  distance  12  miles;  cor.  lat.  at  nooii 
by  observation  37°  52'  X.  Find  ship's  correct  position  at  noon  by 
modern  method. 


Feb.  11-^  12'^  35"^  00«  Decl. 

Fast  -  11     26 


lid  12"  23'"  34''  G.M.T. 


13°  55'  34"  S. 

49".53 

-  10  14 

12.4 

13  45  20  S. 

19812 

90  00  00 

9906 

103°  45'  20" 

4953 

60)614.172 

10'  14" 


Equa.  14"^  26^91 
0.14 


+  14""  26^77 


.012 

12.4 

048 

024 

012 

0.1488 

+ 

S.D. 

16' 

14" 

Pari 

X. 

7 

+  16 

21 

-  6 

21 

+  10' 

00" 

Obs.  alt.    35°  43'  00"  S.D.      16'  14"  Dip,  5'  00" 

10  00  Parlx.  7  Ref.  1   21 


True  alt.  35°  53' 00"  +16  21  —6' 21" 


128  Taylor's  Modern  Xavigation. 

T.  alt.  35°  53' 

Lat.  D.R.    38    00    sec       .10347 

P.D.  103    45    cosec  .01263 

2)177    38 


Half-sum,  88  49  cos  8.31495 
T.  alt.    35  53 


Rem.     52°  56'  sine  9.90197 


2)18.33302 

sine  9.16651 
9.16631 


20A=2«       12'^  00™  2« 
10  52  32 


.T.S. 

ll'J 

22 

52 

30 

+  14 

27 

[.T.S. 

11 

23 

06 

57 

t.T.G. 

11 

12 

23 

34 

10 

43 

23 

4 

60 

180 

)643 

203 

A.T.S. 

10'^  52-^ 

Lat. 

38°  N. 

Decl. 

14°  S. 

Approx.  long,  at  sight,  160°        50'  45"  E. 

■    ) 

T.  az.,  N.  160°  E. 

)  .     180 

s7^  E. 

90 
Cobearing,     70° 
T.  CO.  X.  28°  W.,  12  miles;  D.  lat.  10.6  N".;  dep.  5.6  W. 
Approx.    position  at   sight,     Lat.  38°  00'  N.  Long.l60°50'45"  E. 
D.  lat.  UN.  7  00   W. 


Approx.  position  at  noon,  38   11  N.  160  43  45    E. 

Correct  lat.  at  noon,  37   52  N.     Cor.    1     6  00   W. 

Error  in  lat.       19'  159°37'45"E. 

Cobearing  70°  as  course  and  error  19'  in  lat.  column  give  52.6 
dep.=D.  long.  6Q'  (correction  for  the  long.). 

S..       E. 

N.        W. 


LOXGITUDE.  129 


The  corroct  latitude  being  more  to  the  South,  West  must  be  tlie 
correction  for  the  longitude. 

Example.— ISd A,  March  4th,  a.m.  at  ship,  in  lat.  40°  12'  N.  and 
long.  92°  E.  by  D.K.,  the  following  observation  was  taken  to  ascer- 
tain the  longitude:  Obs.  alt.  of  sun's  L.L.  17°  29';  I.E.  +2'  10"; 
height  of  eye  30  feet ;  time  by  chron.  I''  4'"  51^  which  was  56°»  38« 
slow.  True  course  between  sight  and  noon  S.  36°  E.,  distance  40 
miles;  cor.  lat.  at  noon  39°  57'  X.  Find  ship's  position  at  noon, 
by  modern  method. 

Ih     4m  5p  Decl.  6°  19'  41"  S.  57".8 

+  56     38  9  38  10. 


2    01 
12 

29 

6    29 
90 

P.D.  96°  29' 

0.5 
10. 

05.0 

+ 
I.E.       2'  10" 
S.D.     16   10 
Parlx.           8 

+  18  28 
-   8   25 

+ 10'  03" 

19  S. 
19" 

60)578.0 
9' 38 

March  3^  U""  Ol'" 

Equa.  11'"  50« 
5 

29«M.'r.G. 

+  11'"  55^ 

Alt.      17°  29'  00' 
+  10  03 

Dip,  5'  22" 
Ref.  3     3 

T.  alt.  17°  39' 

-8'  25" 

T.  alt.  17°  39' 

Lat.  DR.    40    12  sec      .11702 

P.D.  96    29  cosec  .00279 


2)154 

20 

Half-s 

um,  77 

10 

cos 

9.34658 

T.  alt. 

17 

39 

Rem. 

59^ 

•  31' 

sine 
2) 

9.93539 

19.40178 

sine 

!  9.70089 

72 

17A  =  6^ 


Taylor's   Mod.   Nav.   9. 


130  Taylor's  Modern  Navigation'. 


12"  0"' 

7  58 

6^ 
56 

A.T.S.  7"  59™ 
Lat.  40°  N. 
Decl.  6°  S. 

A.M.  \            N.115°E. 
VT.az.   180 

S.  65  E. 

3^  19  58 
+  11 

50  A.T.S. 
55 

3  20  10 
3  14  01 

45  M.T.S. 
29  M.T.G. 

90 
Cobearing,   25° 

6   9 
15 

90 

2  15 
4 

16 

Long.  92°  19'  E.  approx.  at  sight. 

T.  CO.  S.  36°  E.  40;  D.  lat.  32.4  S.;  dep.  23.5  K 
Approx.    position   at 

sight,  Lat.     40°  12'  N. 

D.lat.         32^  S. 

Approx.  position  at  noon,     39    39^  N. 
Correct  lat.  at  noon,  39    57   N. 


Long. 

92° 

19' 

E. 

D. 

lonf 

r. 

31 

E. 

92 

50 

E. 

10 

E. 

93° 

00' 

E. 

,0= 

=D. 

long. 

10' 

E. 

Error  in  the  lat.   17yN. 
Cobearing  25°  and  D.  lat.  17 V-'  give  dep.  8.0 
Name  of  sun's  true  azimuth,  S.      yE. 

Opposite  N.^    W. 

Correct  latitude  being  more  to  the  Xorth.  East  must  be  the 
name  of  the  correction,  to  be  applied  to  the  longitude. 

The  ship's  true  position  at  noon  is  therefore  lat.  39°  57'  N. ; 
long.  93°  00'  E. 

Example.— 1894:,  April  27th,  8*^  a.m.  at  ship,  in  lat.  35°  47'  N. 
and  long.  153°  W.  by  D.E.,  the  following  sight  was  taken  to  ascer- 
tain the  longitude:  Obs.  alt.  of  sun's  L.L.  39°  33';  heiglit  of  eye  20 
feet;  time  by  chron.  5"^  22°^  34^  which  was  34'"  22«  slow.  True 
course  S.  72°  W. ;  distance  16  miles,  between  siglit  and  noon;  cor- 
rect lat.  at  noon  35°  18'  N. 


April  27''  5^^  22"^  34« 
+  34  22 

Decl. 

Cor.  decl. 

P.D. 

13°  55'  12" 
+  4  41 

N. 
N. 

47".6 
5.9 

G.M.T.  27"  5"  56"^  56 

13  59  53 
90  00  00 

76°  00'  07" 

4284 
2380 

60)280.84 

4'  41" 


Longitude.  131 


Equa. 

2'"  29^  0.4  Alt.   29°  33'  00" 
2  5.9        +  9  58 

+ 
S.D.  15'  55" 
Parlx.   8 

Dip,  4'  23" 
Ref.  1  42 

- 

-2'"  31^  2.36  T.  alt.  29°  42'  58" 

+  l(i  03 
—  (;  05 

-6'  05" 

+  9'  58" 


T.  alt. 

29°  43' 

Lat.  D.R. 

35  47  sec 

.09085 

P.D. 

2) 

76  00  cos( 

JC.  . 

,01310 

141  30 

Half-sum 

,  70  45  cos 

9. 

51811 

T.  alt. 

29  43 

Rem. 

41°  02'  sin( 
2 

?  9.81723 

)19. 

43929 

sine  9. 

71964 

71952 

^5' 

12A  = 

12'^  0"^ 

5*^ 

7  47 

4 

A.M. 

A.T.S. 
equa. 

M.T.S. 

A.T.S. 

Lat. 
Decl. 

7*^  47"^  A.M.  -j  T.  az. 

26^  19  46 
-  2 

26  19  44 

59 
31 

28 

36°  N.    [  N.  94°  E. 
14  N.    )   180 

S.  86  E. 
90 

Cobearing,   4° 

27  5  56 

56 

M.T.G. 

10  12 

28 

15 

150 

3  7 

Long.  153°  7'  W.  approx.  at  sight. 

T.  CO.  S.  72  °  W.,  16  miles ;  D.  lat.  4.9  S. ;  dep.  15.2  W. 


Approx.  position,  Lat.  35""'  47'  N. 

D.  lat.  5  S. 


Approx.  position  at  noon,  Lat.  35    42   N. 
Correct  lat.  at  noon,  35    18   N. 

Error  in  lat.  24' 


Long. 
D.  long. 

153°  7'W 
19  W 

Long. 
Corr. 

153  26  W. 
2  W. 

153°28'\V, 

132  Taylok's  Modern  Navigation, 


Cobearing  4°  as  course,  with  D.  lat.  24'  in  lat.  column,  gives 
d(-p.  1.7,  which  is  equal  to  2'  D.  long.,  to  be  applied  to  the  approx. 
long,  at  noon  to  obtain  the  correct  long,  at  noon. 

Name  of  sun's  true  azimuth,  S.      E. 
Opposite,  N.     W. 

And  as  the  correct  latitude  is  to  the  South  of  the  incorrect  one. 
West  must  be  the  name  of  the  correction  for  the  longitude. 

The  ship's  true  position  at  noon  is  then  lat.  35°  18'  N.;  long. 
153°  28'  W. 

This  section  would  not  be  complete  without  a  general  considera- 
tion of  the  best  times  to  observe  and  the  errors  likely  to  arise  from 
certain  causes. 

It  will,  no  doubt,  be  remembered  that,  under  the  head  of  "Caution 
to  the  Eising  Generation  of  Navigators,"  the  seaman  was  introduced 
to  the  "extremely  reprehensible  habit"  (Lecky)  of  finding  the  lati- 
tude by  subtracting  the  observed  altitude  from  89°  48',  not  with  the 
hope  or  intention  that  he  would  become  too  familiar,  but  to  quote, 
89°  48'  "is  a  monster  of  so  dreadful  mien 
As,  to  be  hated,  needs  but  to  be  seen," 
^nd,  understood,  to  be  avoided. 

But  to  return  to  the  original  proposition, — the  effect  of  an  error 
in  the  latitude,  and  the  best  times  to  observe. 

An  observation  to  find  the  longitude  ought  to  be  taken  when  the 
sun  is  rising  or  falling  rapidly ;  namely,  when  it  is  about  half-way 
between  the  horizon  and  the  greatest  altitude  it  is  likely  to  attain 
on  the  particular  day  of  observation. 

Do  not  take  the  observation  too  near  noon,  because  the  sun  moves 
more  slowly  in  altitude  as  it  approaches  the  meridian,  and  when 
very  near  it,  its  altitude  will  not  change  to  any  appreciable  extent 
in  one  minute  of  time,  and  as  one  minute  of  time  is  equal  to  15'  of 
longitude,  the  chances  are  that  there  wall  be  a  considerable  error 
in  longitude  if  the  observation  to  find  the  longitude  is  taken  too 
near  noon. 

Do  not  take  the  sight  when  the  sun  is  very  low  (unless  you  have 
no  other  alternative),  as  tlie  refraction  is  a  very  doubtful  quantity, 
and  very  large  when  the  sun  is  near  the  horizon,  but  take  it  when 
the  sun  is  on  or  near  the  Priinc  Verficnl — in  other  words,  when  East 
or  West  true. 


LOXGITUDE.  133 


It  is  not  always  possible  to  take  a  sight  when  the  sun  bears  East 
or  West,  as  it  entirely  depends  on  the  latitude  of  the  observer  and 
the  declination  of  the  sun,  but  the  observer  should,  if  possible,  al- 
ways take  the  sight  when  the  sun  is  on  or  near  the  Prime  Vertical. 

This  may  be  determined  in  the  following  manner,  with  the  as- 
sistance of  the  American  Azimuth  tables : 

EULE. 

Open  the  tables  to  the  nearest  degree  of  latitude,  being  careful  to 
notice  if  the  latitude  and  declination  have  the  same  name  or  contrary 
names;  look  under  the  nearest  degree  of  declination  until  90°  is 
found,  then  note  the  time  abreast  in  either  the  a.m.  or  p.m.  columns 
at  the  sides;  this  will  give  the  time  of  the  sun's  passage  over  the 
Prime  Vertical,  which  is  the  best  time  to  take  a  sight  to  find  the 
longitude;  but  if  90°  cannot  be  found,  take  the  time  abreast  of  the 
nearest  number  of  degrees,  and  this  will  be  the  best  time  to  observe, 
under  the  circumstances. 

The  object  of  taking  the  sight  when  the  sun  is  on  the  Prime  Ver- 
tical is,  if  there  is  an  error  in  the  latitude,  it  produces  no  error  in 
the  longitude,  and  if  it  is  not  possible  to  get  a  Prime  Vertical  sight, 
take  one  as  near  to  it  as  possible,  for  the  reason  that  the  nearer  the 
sun's  bearing  approaches  the  true  East  or  true  West,  the  smaller  will 
be  the  error  in  the  longitude  produced  by  an  error  in  the  latitude. 

By  referring  to  the  three  modern  a.m.  sights  worked  out  in  full, 
these  conditions  are  exemplified,  for  one  of  them  has  a  large  cor- 
rection to  be  applied  to  the  longitude  because  the  bearing  at  time 
of  sight  was  a  long  way  from  East  or  West  true.  The  other  is  a 
Prime  Vertical  sight,  nearly,  and  has  only  a  very  small  correction 
to  be  applied.  These  examples  were  selected  on  purpose  to  illustrate 
the  facts  herein  stated,  and  may  be  proven  by  working  the  old- 
fashioned  method. 

It  therefore  behooves  the  navigator  to  be  careful  to  use  the  cor- 
rect latitude,  and  not  the  lazy  89°  48'  proposition  to  obtain  it. 

The  lazy  method  of  finding  the  latitude  is  most  dangerous  during 
the  winter  months,  as  during  this  season  the  sun  does  not  come  any- 
where near  the  Prime  Vertical,  and  does  not  rise  very  high ;  re- 
fraction will  be  large  and  of  a  doubtful  quantity,  and  an  error  in 
the  latitude  at  this  time,  when  used  to  find  the  longitude,  may  pro- 
duce, under  certain  conditions,  as  much  as  28'  or  30'  of  an  error 
in  the  longitude.  The  mischief  does  not  stop  here,  for  if  the  navi- 
gator is  steering  in  for  the  land  with  the  intention  of  making  a  cer- 


134  Taylor's  Moderx  ^s'avigation. 


tain  point,  he  may  find  liis  vessel  considerably  out  of  her  intended 
position,  and  he  may  consider  himself  lucky  if  he  keeps  her  afloat, 
by  the  extraordinary  vigilance  of  the  lookout-man,  provided,  of 
course,  the  weather  is^  clear,  so  that  a  good  lookout  can  be  kept. 

The  navigator  (God  save  the  mark !),  of  course,  would  blame,  for 
any  accident  that  might  occur,  bad  steering,  inattention  of  the  deck- 
officer,  or  some  sudden  change  in  the  deviation  of  his  compass,  or 
ur known  current,  but  we,  behind  the  scenes,  know  the  reason,  and 
he  ought  to. 


DIVISION  YI. 

LONGITUDE    BY  FIXED    STAKS. 

To  the  time  shown  by  chronometer  apply  the  error,  if  any,  and 
obtain  the  G.M.T.  the  same  as  for  the  sun.  Correct  the  star's  ob- 
served altitude  for  index  error,  if  any,  and  for  dip  and  refraction. 

Enter  the  Nautical  Almanac  and  take  from  page  2  of  the  month 
(at  Greenwich  Mean  Noon),  abreast  of  the  Greenwich  date,  the 
sidereal  time  or  right  ascension  of  mean  sun.  Correct  this  sidereal 
time  by  entering  Table  3,  at  the  end  of  the  Nautical  Almanac,  with 
the  hours  and  minutes  of  G.M.T.,  and  take  therefrom  the  mean 
time  interval,  which  must  always  be  added  to  the  sidereal  time  at 
noon  to  obtain  the  reduced  sidereal  time. 

Next  enter  table  of  fixed  stars,  and  abreast  of  star's  name  take  out 
and  mark  down  its  right  ascension  (R.A.),  and  let  it  stand  as  it  is. 

Now  take  the  star's  declination  and  mark  it  North  if  -{-,  but 
South  if  — ,  and  find  the  polar  distance  by  the  usual  rule. 

Mark  down  the  true  alt.,  lat.,  and  P.D.,  add  them,  divide  the 
sum  by  2,  and  subtract  from  the  half-sum  the  true  alt.  Next  take 
the  secant  of  lat.,  cosecant  P.D.,  cosine  half-sum,  sine  remainder, 
add  these  four  logs.,  and  divide  the  sum  by  2  ;  this  half-sum  of  logs, 
will  be  the  log.  sine  of  the  sidereal  time  at  ship. 

If  the  star  observed  is  West  of  the  meridian,  take  the  time  from 
the  P.M.  column ;  but  if  East  of  the  meridian,  take  the  time  from 
the  A.M.  column  and  add  12  hours  to  it.  In  either  case  the  result 
will  be  the  sidereal  time  at  ship. 

To  this  sidereal  time  at  ship  add  the  right  ascension  (R.A.)  of 
the  star,  rejecting  24  hours  if  necessary.  The  result  will  be  the 
right  ascension  of  the  meridian  (R.A.  of  mer.). 

From  the  R.A.  of  mer.  subtract  the  reduced  sidereal  time,  borrow- 
ing 24  hours  if  necessary.     The  result  will  be  the  M.T.S. 

If  the  hours  of  the  M.T.S.  are  fewer  than  12,  prefix  the  civil 
date;  if  more  than  12,  prefix  yesterday's  date.  The  result  will  be 
the  astronomical  mean  time  at  ship. 

Now  take  the  difference  between  the  M.T.S.  and  M.T.G.  The 
result  will  be  the  longitude  of  the  ship  in  time,  which  must  be  con- 
verted into  longitude  by  the  rule  used  in  any  of  the  preceding  ex- 
amples when  finding  the  longitude. 

All  star  and  planet  observations  here  given  are  worked  to  nearest 
minutes  of  arc  only,  which  is  sufficiently  near  for  all  practical  pur- 
poses. 


136  T-VYLOirs  Moderx  Xavigatiox. 

Longitude  by  Altair. 
Example. — 1894,  May  21st,  1  o'clock  a.m.  at  ship,  in  lat.  27°  5' 
X. ;  long.  146°  7'  W.  by  D.R. ;  obs.  alt.  of  star  Altair  East  of  merid- 
ian 40°  48';  I.E.  — 2'  lU";  height  of  eye  20  feet;  time  by  chron. 
10*^  SO""  25^  which  was  fast  lO'"  50«  for  M.T.G.  Find  the  longi- 
tude at  time  of  sight. 
Mav  20"^  22'^  30«^  25^  R.A.  3'^  52">  3P 

10     50  +   3     40  (Table 3, N. A.) 

20*^  22^  19™  35^  G.M.T.  3"  56"'  IP  red.  sid.  time 

Star's  obs.  alt.  40°  48'  00"  I.E.   2'  10" 

-      7  40  Dip,  4  23 


T.  alt.  40°  40'  20' 


Ref.  1     7 


7'  40' 


Star's  decl.    8°  35'  19"  N. 
90    00  00    N. 


P.D.  81°  24'  41" 

Star's  R.A.  19^  45™  37^ 
T.  alt.         40°  40' 
Lat.  27    05    sec       .05044 

P.D.  81    25    cosec  .00489 


2)149    10 


Half-sum,  74  35  cos  9.42461 
40  40 


33  55  sine  9.74662 


2)19.22656 


sine  9.61328  =  20'^  46 
20"  46™  07«  sid.  T.S. 
-19    45     37 


Rejecting  24  hours,       16    31     44    R.A.  of  mer. 
3    56     11    red.  sid.  time. 


May  20"  12  35  33    M.T.S. 

May  20   22  19  35    M.T.G. 

9  44  02    long,  in  time. 
15 

135 

11  00  30 


l.oiitr.  146°  00'    30"  \V.  at  sight, 


LOiNGlTUDli.  137 


J^OXGITIDE    BY    VeGA. 

Example.— 1S94,  April  25th,  at  10  p.m.  at  ship,  in  lat.  34°  55' 
N.;  long.  143°  30'  E.  by  D.R.;  obs.  alt.  of  star  Vega  24°  28'  East 
of  meridian;  I.E.  —1'  30";  height  of  eye  30  feet;  time  by  chron. 
1"  15'"  55%  which  was  fast  12'"  20-^  for  G.M.T.  Find  longitude  of 
ship  at  time  of  sight. 


April  25"  1"  15'"  55^     Sid.  time  2"  13'"  57« 

Fast        -    12    20  +      10  (Interval,  Table  8,  N. A.) 

April  25**  P  03'^^  35^  M.T.G.        2*^  14""  07«  red.  sid.  time. 


Star's  R.A.  18"  33"'  2P. 


Star's  decl.  38°  41'    6"  N. 
dO   00  00 


P.D.  51°  18'  54" 


Star's  obs.  alt.  24°  28'  00"         I.E.     1'  30" 
8  00  Dip,    4  23 

T.  alt.  24°  20'  00"         ^^^-    1^ 


-  8'  00" 


T.  alt.        24°  20' 

Lat.  34    55    sec        .08619 

P.D.  51    19    cosec     .10756 

2)110    34 
Half-sum, 55    17    cos      9.75551 
T.  alt.        24    20 
Rem.         30°  57'  sine     9.71121 
2)19.66047 


sine     9.83023  =  6"  19'"  28^ 


138  Taylor's  Modern  Navigation. 


6"  19'"  28^* 
12 


18    19     28    sid.  time  at  ship. 
+  18    33     21    R.A.  of  Vega. 


Rejecting  24  hours,       12    52     49    R.A.  of  mer. 
—   2     14     07    red.  sid.  time. 


April  25    10    38     42   M.T.8. 
April  25      1    03     35    M.T.G. 


9" 

35>"  07« 

long,  in  time, 

15 

135 

8 

45 

1  45 

Lons.   143°  46'  45"  E.  at  time  of  sight. 


LONGITUDE  BY  PLANET. 


Correct  the  planet's  declination. 

Open  the  Nautical  Almanac  under  the  planet's  name,  at  the  end 
of  the  Almanac.  Search  for  the  month  on  top  and  the  date  at  the 
side,  and  abreast  of  the  date  take  out  the  planet's  declination,  and 
its  variation  for  one  hour,  multiplying  it  by  the  hours  and  tenths  of 
hours  of  G.M.T.,  the  same  as  when  correcting  the  sun's  declination. 

Correct  the  planet's  right  ascension  in  same  manner. 

The  remainder  of  the  problem  is  identical  with  that  of  a  star. 

Longitude  by  Planet  Jupiter. 

Example. — 1894,  November  iSth,  ()''  20™  a.m.  at  ship,  in  lat. 
25°  26'  N.;  long.  126°  W.  by  D.R.;  obs.  alt.  of  planet  Jupiter 
(center)  45°  24'  50"  West  of  meridian;  I.E.  —2'  00";  height  of 
eye  26  feet;  time  by  chron.  3*^  19""  30%  which  was  fast  ll'"  30^  for 
M.T.G.     Find  longitude  of  ship  at  time  of  sight. 


Nov. 

(i"  3"  19" 

'  30« 

Dec! 

1. 

23^  00'  12"  N. 

0".55 

14 

30 

r.(;. 

Cor. 

(brl 

-[-    1 

3.1 

Nov. 

<•)'•  3"  05" 

■  00^  M.' 

.  23  00  13 

050 

90  00  00 

150 

P.I).  6B°  59' 47"  1".550 


Longitude.  139 


Planet's  R.A.  (i"  2(V"  17^(i7         0.506         Sid.  time,       15''  2'"  45^ 
1  M         3.1  Sid.  interval,  +30 


Cor.  R.A.  (5"  26"'  16M1         0506         Red.  sid.  T.     15"  3'"  10« 

1518 


1.5686 


Obs.  alt.  45°  24'  50"  I.E.    2'  00" 

-  7   58  Dip,  5  00 


True  alt.  45°  16'  52' 


Ref.        58 


7' 58' 


T.  alt.     4.5° 

17' 

Lat.      25 

26 

sec 

.04427 

P.D.      67 

00 

cosec 

.03597 

2)137 

43 

Half-sum,  68 

51 

cos 

9.55728 

T.  alt.     45 

17 

sine 

Rem.     23° 

34' 

9.60186 

2 

)  19.23938 

sine 

9.61969 

1« 

9.61966 

3'^  16'"  56  3A  =  p 

S^  16°'  57**  hour-angle,  or  sid.  time  at  ship. 
+   6    26     16    cor.  R.A.  of  Jupiter. 

9    43     13    R.A.  of  Mer. 
—  15      3     15    red.  sid.  time. 


Nov.  5    18    39     58   M.T.S. 
Nov.' 6     3    05     00   M.T.G. 


8 

25  02 

15 

140 

6 

15 

0  30 

Long.   146°  15'    30"  W.  at  time  of  sight. 


140  Taylor's  Modern  Navigation. 


Examples  for  Practice. 

189-i,  May  22d,  5*^  20°^  a.m.  at  ship,  in  lat.  24°  5'  N.;  long.,  by 
D.R.,  152°  30'  W.;  obs.  alt.  of  planet  Venus  East  of  meridian 
28°  12';  I.E.  +3'  20";  eye  26  ft.;  time  by  chron.  3"^  25°^  30%  which 
was  fast  14™  35^  for  M.T.G.  Find  the  longitude  of  ship  at  time  of 
sight. 

Answer.— Decl.  4°  54'  28"  N.;  E.A.  1^  5°^  54^;  sid.  T. 
4h  Qm  55s.  rp  ^^^_  28°  8'  51";  long.  152°  47'  W. 

1894,  April  28th,  O''  10"°  a.m.  at  ship,  in  lat.  33°  34'  20"  X. ;  long. 
164°  20'  E.  by  D.R. ;  obs.  alt.  of  star  Eegulus  West  of  meridian 
26°  15'  00";  I.E.— 2'  10";  eye  19  ft.;  time  by  chron.  1"  6°^  30% 
which  was  slow  2'"  20^  for  M.T.G.  Find  the  longitude  at  time  of 
sight. 

Answer.— Decl.  12°  29'  6"  X.;  T.  alt.  26°  6'  36";  E.A.  10*^  02'" 
44«;  sid.  T.  2^  22""  OP;  long.  164°  45'  45"  E. 

1894,  August  9th,  a.m.  at  ship,  in  lat.  24°  5'  50"  X.;  long.,  by 
D.E.,  156°  24'  W.;  obs.  alt.  of  star  Eigel  East  of  meridian  32°  35' 
00" ;  I.E.  +3'  40" ;  eye  20  ft. ;  time,  by  chron.  3"^  15"^  20%  which 
was  fast  7"^  40^  for  G.M.T.    Find  the  longitude  at  time  of  sight. 

Answer.— Decl.  8°  19'  28"  S.;  T.  alt.  32°  32'  46";  E.A.  5^^  09°» 
27«;  sid.  T.  9»^  12°^  23%  long.  156°  16'  15"  W. 

1894,  January  16th,  5  a.m.  at  ship,  in  lat.  30°  15'  N. ;  long.,  by 
D.E.,  145°  10'  W.;  obs.  alt,  of  planet  ^Mars  (center)  East  of  merid- 
ian 16°  48'  00";  I.E.  +3'  40";  eye  22  ft.;  time  by  chron.  S^  6"^ 
53%  which  was  7°*  13«  fast  for  M.T.G.  Find  the  longitude  of  ship 
at  time  of  sight. 

Answer.— P.D.  111°  55'  55";  T.  alt.  16°  44'  00";  planet's  E.A. 
16^  36™  07;  red.  sid.  T.  19»^  44""  08%  E.A.  of  mer.  13''  Ol""  55% 
long.  145°  28'  15"  W 

1894,  March  11th,  5''  40^"  a.m.  at  ship,  in  lat.  12°  20'  N. ;  long., 
by  D.E.,  166°  15'  E.;  obs.  alt.  planet  Saturn  (center)  34°  10'  50" 
West  of  meridian;  I.E.  +3'  20";  eye  21  ft.;  time  by  chron.  6"  40°» 
10%  which  was  slow  5°'  12^  for  M.T.G.  Find  the  longitude  of  ship 
at  time  of  sight. 

Answer.— P.D.  96°  48'  33";  planc't's  E.A.  13'>  33°^  12';  red.  sid. 
T.  23''  13"'  41%  T.  alt.  34°  8'  16";  E.A.  of  mer.  17"  04"'  2(1%;  long. 
166°  20'  30"  E. 

1894,  October  22d,  5''  30"'  a.m.  at  ship,  in  lat.  21°  26'  00"  N. ; 
long.,  by  D.E.,  160°   10'  W. ;  obs.  alt.  of  star  Aldt'barnn   West  of 


Longitude.  141 


meridian  4(J°  15'  U"  ;  eye  25  ft.;  J.E.  +;}'  2(»";  time  by  chron.  4'' 
2'"  1U^  which  was  slow  7'"  5^  for  M.T.G.  Find  the  longitude  of 
ship  at  time  of  sight. 

Answer.— P.D.  73°  42'  15";  E.A.  of  star  4"  29'"  50«;  sid.  T. 
14h  4m  i8«;  E.A.  of  Mer.  7"  34">  IT**;  T.  alt.  4()°  12'  30";  long. 
159°  48'  45"  W. 

Remarks  ix  Regard  to  Star  and  Planet  Observations  avuen 
Taken  to  Find  the  Longitude. 

Many  seamen  are  of  the  opinion  that  observations  of  stars  and 
planets,  when  used  to  ascertain  longitude,  involve  a  very  lengthy 
and  therefore  tedious  calculation,  requiring  an  exceedingly  pro- 
found knowledge  of  mathematics  and  trigonometry.  This  is  not 
so,  for  any  one  that  can  work  a  sun-sight  can  also  work  a  stellar 
observation  if  he  is  willing  to  learn ;  and,  by  the  way,  a  word  in  the 
ear  of  those  that  are  not  very  fond  of  work;  star-sights  have 
fewer  figures  than  sun-sights,  and  are  extremely  easy  to  learn. 

Seamen  will,  no  doubt,  remember  numerous  instances  when  it 
was  not  possible  to  observe  the  sun,  by  reason  of  cloudy  or  foggy 
weather,  but  when  night  came  on  and  the  weather  cleared,  quite  a 
number  of  good  navigational  stars  were  visible  to  choose  from, 
whereas  if  dependence  is  placed  entirely  on  "t)ld  Sol,"  he  may  be 
obscured  at  the  most  desirable  time,  and  the  navigator  would  then 
have  to  calculate  by  dead-reckoning,  which  is  bad,  even  at  its  best. 

There  are  plenty  of  stars  always  visible  on  a  fairly  clear  night, 
which  may  be  observed  for  both  latitude  and  longitude,  but  there  is 
only  one  sun  to  observe  during  the  day. 

The  following  case  in  point,  relating  to  the  usefulness  of  star- 
observations,  will,  no  doubt,  be  duly  appreciated. 

The  run  between  sight  and  noon,  or  noon  and  sight,  according 
as  it  is  an  a.m.  or  p.m.  observation  of  the  sun,  may  be  almost  en- 
tirely dispensed  with  when  the  stars  are  observed,  for  it  is  possible 
to  select  a  star  to  the  Xorth  or  South  for  latitude,  and  another  to 
the  East  or  \Yest  for  longitude. 

Make  the  latitude  observation  first  and  the  longitude  second,  and 
as  nearly  simultaneous  as  possible;  thus:  Have  two  sextants,  and  an 
assistant  "standing  by"  the  chronometer.  Measure  the  meridian 
altitude  of  a  star  nicely  and  lay  the  sextant  down;  you  have  plenty 
of  time  to  read  it  afterwards.  As  soon  as  this  is  done,  pick  up  the 
other  sextant  and  observe  a  star  for  longitude,  and  note  the  chro- 
nometer time;  work  up  the  latitude,  then  the  longitude,  and  the 


142  Taylor's  Moderin  Xavigatiox. 

ship's  true  position  is  found,  with  the  doubt  in  regard  to  the  true 
course  and  distance  entirely  eliminated.  This  pointer  will,  of 
itself,  be  a  sufficient  recommendation  of  the  value  of  star-observa- 
tions. 

The  best  time  to  observe  is  when  the  horizon  is  well  defined  and 
when  the  object  is  on  or  near  the  prime  vertical.  As  before  ex- 
plained, good  results  will  be  had  if  the  observer  is  persistent  and 
does  not  expect  too  much  at  first;  for  practice  will  make  him  per- 
fect in  measuring  the  altitude. 

WHAT  TO  DO  WHEN  CROSSING  THE  MERIDIAN  OF  180°, 

AND  OTHER  MATTERS  RELATING  TO  THE 

CHANGE  OF  TIME. 

It  is  presumed  that  the  student  is  by  this  time  thoroughly  fa- 
miliar with  the  various  methods  of  determining  the  longitude  by 
chronometer,  yet  he  would,  no  doubt,  become  confused  in  their 
practical  application  if  the  following  were  omitted: 

There  are  360°  of  longitude  in  all,— 180°  of  East  and  180°  of 
West  longitude. — both  of  them  meaning  one  and  the  same  place, 
namely,  the  opposite  meridian  to  that  of  Greenwich. 

360°  divided  by  24  hours  gives  15°;  therefore  15°  is  equal  to  1 
hour  of  time,  and  1°  equals  4  minutes  of  time. 

It  will  be  remembered  that  when  a  ship  is  in  East  longitude  her 
time  is  ahead  of,  and  when  in  West  longitude  her  time  is  behind, 
that  of  Greenwich,  always  to  the  amount  of  her  longitude  in  time. 

Now,  it  must  be  understood  that  as  a  vessel  moves  to  the  East  or 
to  the  West  her  time  will  change  according  to  the  amount  of  dif- 
ference of  longitude  she  makes  good,  gaining  if  traveling  to  the 
East,  losing  if  traveling  to  the  West,  as  will  be  seen. 

A  vessel  going  East  moves  towards  the  sun,  and  the  sun  moves 
towards  the  ship.  This  is  not  theoretically  correct  in  regard  to  the 
sun,  but  we  will  assume  it  is  so,  for  the  sake  of  illustration.  Now, 
this  vessel,  for  every  15°  she  moves  to  the  East,  meets  the  sun  one 
hour  earlier  each  day ;  that  is,  the  sun  would  rise  earlier  and  arrive 
at  its  meridian  altitudo  earlier  by  one  hour  for  every  15°  the  ship 
sailed  to  the  East. 

If  the  ship  sailed  West,  the  contrary  wouhl  be  the  result;  namely, 
for  every  15°  she  sailed  West  it  wouhl  take  the  sun  one  hour  longer 
to  catch  up  with  the  ship. 

Now,  suppose  the  ship  sailed  from  New  York  to  the  l^'ast  15°; 


Longitude.  143 


her  time  would  be  one  hour  ahead  of  New  York  time;  that  is,  if  it 
was  9  A.M.  at  New  York  it  would  be  10  a.m.  at  ship. 

Hut  if  she  sailed  15°  to  the  West,  then  her  time  would  be  one 
hour  behind  New  York  time;  that  is,  if  it  was  9  a.m.  at  New  Y'ork 
it  would  be  8  a.m.  at  ship. 

It  will  therefore  be  very  evident  that  as  the  ship  sails  East  her 
days  become  shorter,  and  if  she  continues  sailing  to  the  East  until 
she  has  made  the  entire  circle  of  the  world,  when  she  arrives  at  New 
York  it  will  be  found  by  those  on  board  that  they  have  gained  one 
whole  day,  or  24  hours.  The  ship's  date  would  then  be  one  day 
ahead  of  the  Xew  Y^ork  date,  that  is,  if  it  was  Sunday,  March  17th, 
at  New  York,  it  would  be  Monday,  March  18th,  according  to  the 
reckoning  of  those  on  board. 

Now,  if  it  were  possible  that  this  ship  had  sailed  to  the  West  in- 
stead of  to  the  East,  and  made  also  a  round  turn  of  the  world,  she 
would  find  on  her  arrival  at  New  York  that  her  date  would  be  one 
day  behind;  that  is,  if  it  was  March  17th  at  New  Y^ork,  it  would  be 
March  16th  with  those  on  board.  These  two  cases  are  what  might 
occur  to  any  one  not  changing  the  date  w^hen  crossing  the  180th 
meridian. 

Thus  a  vessel  after  sailing  East  and  arriving  at  180°  of  longitude 
would  find  her  time  to  coincide  with  Greenwich  time;  but  with  this 
difference,  her  time  would  be  12  hours  ahead  of  Greenwich ;  that 
is,  if  it  was  noon  at  ship  it  w^ould  be  midnight  of  last  night  at 
Greenwich ;  but  if  she  had  sailed  West,  her  time  would  coincide  with 
that  of  Greenwich  again,  but  12  hours  behind;  that  is,  if  it  was 
noon  at  ship  it  would  be  midnight  of  next  night  at  Greenwich.  The 
word  coincide  means  that  the  ship's  clock  time  would  be  the  same 
as  chronometer  time. 

It  is  therefore  very  necessary  for  the  navigator  to  attend  to  liis 
date  when  crossing  the  180th  meridian,  and  the  following  is  the 
rule : 

If  sailing  to  the  eastward  and  arriving  at  180°,  hold  the  date  one 
day  back;  thus  if  the  ship  arrive  at  the  meridian  at  10  a.m.  on 
Sunday,  May  3d,  call  the  next  day  Sunday.  May  3d.  also. 

If  she  is  sailing  to  the  West,  jump  over  a  day ;  thus  if  ship  arrives 
at  meridian  some  time  on  Saturday,  May  2d,  call  tlie  next  day  :Mon- 
day.  May  4th.  Now,  it  must  not  be  supposed  that  the  time  has  been 
changed  24  hours,  for  such  is  not  the  case  in  reality ;  only  the  date 
changed,  for  the  vessel,  sailing  to  the  East,  has  gained  12  hours, 
and  by  holding  the  date  one  day  back,  the  effect  of  gaining  one  day 


144  Taylok's  Modern  Navigation. 


when  making  the  circle  of  the  world  is  counteracted  by  the  time  sho 
arrives  at  the  place  of  departure.  The  result  when  sailing  West  is 
the  contrary  of  the  above,  as  by  the  time  the  ship  arrives  at  180°  she 
must  have  lost  12  hours,  and  the  result,  in  this  case,  of  a  vessel 
making  the  circle  of  the  world  would  be  that  of  losing  one  day ; 
therefore  this  is  counteracted  by  jumping  over  a  day. 

Little  Pointers,  which.  Although  not  Relating  to  the 
Crossing  of  the  180th  Degree  of  Longitude,  still  have 
Considerable  Bearing  on  it. 

Bule  to  Set  Ship's  Wheelhouse  Clod  so  that  It  will  Indicate  Ap- 
proximately Twelve  Hours  when  the  Meridian  Altitude  is  Observed. 
— On  board  of  sailing-ship,  most  seamen  have  noticed  a  consider- 
able discrepancy  in  the  time  shown  by  the  clock  and  the  moment  of 
striking  eight  bells;  this  is  all  very  well  for  the  windjammer,  al- 
though the  cook  and  steward  may  kick  about  the  dinner  being 
spoiled,  but  it  will  not  do  for  an  ocean  steamer,  for  there  are  too 
many  people  to  be  considered;  therefore  clocks  on  board  must  be 
set  at  some  time  when  it  will  least  inconvenience  those  on  board. 

To  proceed,  suppose  that  we  are  bound  from  San  Francisco  to 
China,  and  therefore  sailing  to  the  West.  The  ship  would  be  losing 
time  each  day,  according  to  the  amount  of  difference  of  longitude 
in  time  she  makes  between  noons  of  two  consecutive  days. 

If  she  made  7°  of  diff.  of  long.,  she  would  have  lost  28  minutes, 
and  her  actual  running  time  between  noon  of  yesterday  and  to-day 
would  be  actually  24^  28™,  and  if  the  ship's  clock  had  not  been 
altered,  which  it  ought  to  have  been,  it  would  indicate  28  minutes 
past  12  when  the  sun  was  on  the  meridian. 

Now,  if  this  ship  had  been  sailing  East  this  7°  (from  China  to 
San  Francisco),  she  would  have  gained  28  minutes,  and  the  actual 
running  time  between  noon  of  yesterday  and  to-day  would  be  23*' 
32™.  In  this  case,  if  the  ship's  clock  had  not  been  attended  to,  the 
navigator  would  be  28  minutes  too  late  for  the  meridian  altitude. 

The  preceding  remarks  will  direct  the  attention  of  the  student 
to  the  fact  that  there  is  something  to  be  done  to  the  clock,  and  the 
following  is  the  rule: 

Rule. 

The  bridge-officer  having  the  watch  from  8  to  12  p.m.  must,  a  lit- 
tle before  midnight,  calculate  approxinuitcly,  by  D.K.,  tlie  amount 


Longitude.  145 


of  diff.  of  long,  in  time  the  vessel  will  make  from  last  noon  to  next 
day  at  noon,  and  if  sailing  to  the  East  he  must  put  the  clock  ahead 
this  amount,  but  if  going  West  he  must  put  the  clock  back  this 
amount,  dividing  the  time  between  his  watch  and  the  next.  After 
being  relieved  at  eight  bells  he  must  proceed  to  the  saloon  and  set 
the  clocks  there,  then  to  the  engine-room  and  inform  the  engineer 
on  watch,  who  will  set  the  engine-room  clock  so  that  it  tallies  with 
the  deck  time,  the  bridge-officer  entering  in  the  wheelhouse  log-book 
tlie  amount  of  change,  and  the  engineer  entering  it  in  the  engine- 
room  log-book. 

If  the  above  is  properly  carried  out,  all  clocks  on  board  will  indi- 
cate 12,  very  nearly,  when  the  sun  is  on  the  meridian. 

To  Find  the  Length  of  Passage  of  an  Ocean  Greyhound. 

Xote  the  civil  date  and  time  at  the  instant  of  departure,  and 
state  it  astronomically. 

Note  the  civil  date  and  time  at  arrival,  and  state  it  astronomi- 
cally also.  , 

Take  the  difference  between  the  two  by  subtracting  one  from  the 
other.     The  result  will  be  the  apparent  length  of  passage. 

Find  the  difference  of  longitude  between  the  place  of  departure 
and  that  of  arrival  and  convert  it  into  time. 

Add  this  difference  of  longitude  in  time  to  the  apparent  length 
of  passage  if  ship  has  sailed  to  the  West,  but  subtract  if  she  has 
sailed  to  the  East.  The  result  in  either  case  will  be  the  mean  length 
of  time  the  ship  occupied  on  the  passage  between  the  port  of  de- 
parture and  that  of  arrival. 

The  reason  why  the  difference  of  longitude  in  time  is  subtracted 
when  the  ship  sails  East  is  that  there  is  actually  less  time  than  24 
hours  in  each  day,  because  of  her  gaining  time ;  and  the  reason  why 
the  difference  is  added  when  sailing  West  is  because,  losing  time, 
her  apparent  days  are  more  than  24  hours  long.  When  sailing 
East,  her  apparent  length  of  passage  is  too  great,  and  when  sailing 
West,  too  small. 

Example. — Passed  Fort  Point,  San  Francisco,  in  long.  122°  29' 
W.,  on  January  16th,  at  6**  20°*  a.m.  Arrived  at  Honolulu,  Ha- 
waiian Islands',  in  long.  157°  22'  W.,  on  January  22d,  at  1^  40'' 
P.M.     Eequirod  the  mean  length  of  passage. 

Taa'LOR's   Mod.   Nav.   10. 


146  TAYLOifs  Modern  Xavigation. 


Fort  Point,  ast.  timf,  Jan. 
Honolulu,    ast.  time,  Jan. 

,  15*^  1<S'>  2U" 
22     7    40 

'  U0« 
00 

Long.  122°  29' 
Long.  157    22 

34    53 
4 

W 
W. 

A  pp.  length  of  passage, 
Diff.  of  long,  in  time, 

6    13    20 
+   2    19 

00 
32 

Mean  length  of  passage, 

6**  15''  39°' 

32« 

60)139    32 

2'M9'"32« 

Example. — Passed  Sandy  Hook  light-ship,  in  long.  74°  W.,  on 
April  21st,  at  10''  32°'  a.m.  Arrived  off  the  Fastnet  Rock,  in  long. 
9°  36'  W.,  on  April  27th,  at  2"  5"'  a.m.  Required  the  mean  length 
of  passage. 

Sandy  Hook,  ast.  time,  April  20''  22"  32"'  00^       Long.  74°  00'  W. 
Fastnet  Rock,  ast.  time,  April  26    14      5     OU        Long.    9    36   W. 

App.  length  of  passage,  5    15    33     00  64    24 

Diff.  of  long,  in  time,  —  4    17     36  4 

Mean  length  of  passage,  5"  11"  15"'  24-^  60)257    36 

4"  17"^  36« 


DIVISION  Ml. 

SUMNER'S  METHOD  OF  FINDING  THE  LATITUDE  AND 
LONGITUDE. 

Like  many  other  useful  discoveries,  tliis  method  was  actually 
stumbled  upon  by  Captain  Sumner,  an  American  ship-master,  and 
a  very  lucid  account  of  the  occurrence  is  given  in  the  Bowditch 
Epitome,  which  we  advise  the  student  to  read. 

The  Ohsercation. — Take  two  chronometer  observations,  one  in 
the  forenoon  and  one  in  the  afternoon,  or  both  in  the  morning  or 
both  in  the  afternoon  if  they  are  not  too  close  together,  being 
careful  to  note  the  true  course  and  distance  sailed  between  sights. 

Select  two  latitudes,  one  on  each  side  of  where  you  think  the  ship 
is. 

The  Computation. — Work  the  first  observation  with  these  two 
latitudes,  and  mark  them  A  and  B. 

Next  work  the  second  observation  with  the  same  two  latitudes, 
and  mark  them  C  and  D. 

Then  select  a  chart  having  the  proper  latitudes,  and  mark  on  it 
the  first  two  longitudes,  A  and  B,  on  their  respective  latitudes; 
draw  a  line  of  indefinite  length  through  them,  and  name  this  line 
the  First  Line  of  Position,  and  the  ship  will  be  somewhere  on  this 
line  at  time  of  taking  the  first  sight. 

From  any  part  of  this  first  line  of  posipon  lay  off  the  true 
course  and  distance  the  ship  sailed  between  sights,  and  through  the 
end  of  this  course  and  distance  line  draw  another,  parallel  to  the 
first  line  of  position,  and  name  it  the  Projected  Line. 

Now  mark  on  the  chart  the  second  two  longitudes  on  their  re- 
spective latitudes  and  draw  a  line  of  indefinite  length  through 
them.  This  last  line  is  called  the  second  line  of  position,  and  as 
the  ship  is  somewhere  on  this  line,  and  also  somewhere  on  the  pro- 
jected line,  at  the  instant  of  taking  the  second  sight,  the  point  where 
they  intersect  or  cross  each  other  will  be  the  position  of  the  ship. 

The  second  and  projected  lines  must  always  cross,  but  if  tliey  do 
not,  extend  them  until  they  do. 

A  very  important  item  to  renu'inl)cr  in  relation  to  the  lines  of 
position  is  that  the  sun's  true  bearing  may  be  found  by  striking  a 
right  angle  to  either  one  of  them,  to  the  east  if  an  a.:m.  sight,  and 
tii  the  West  if  a  p.m.  sight;  therefore  if  at  the  time  of  taking  the 


148  Taylor's  Modern  Navigation. 

observations  the  observed  bearing  of  tlie  sun  and  the  direction  of 
the  ship's  head  has  been  noted,  the  deviation  may  be  found,  as  well 
as  ship's  position. 

Example  for  Practice. 

1894,  September  25th  7  a.m.  at  ship,  and  uncertain  of  my  posi- 
tion; a  chronometer  showed  1^  6""  S**  G.M.T.,  and  at  same  instant 
the  sun's  obs.  alt.  L.L.  was  10°  49'  20= ;  the  ship  then  sailed  S.  62° 
E.  true,  27  miles,  when  the  following  sight  was  taken:  At  3  p.m. 
at  ship,  same  day,  chronometer  showed  2>^  00™  30^  G.M.T.,  when 
the  obs.  alt.  sun's  L.L.  was  26°  46'  40",  and  height  of  observer's 
eye  at  both  observations  10  feet.  The  ship,  by  D.R.,  was  estimated 
to  be  between  the  latitudes  of  46°  58'  J^T.  and  46°  20'  N.,  and  long., 
by  D.R.,  about  179°  E.  Required  the  latitude  and  longitude  of 
ship  at  time  of  taking  the  second  observation,  and  the  sun's  true 
azimuth  at  both  first  and  second  sights. 

First  Observation. 


1894, 
Decl. 

Sept.  24^  7 

0°  33'  41" 
+  6  55- 

s. 
s. 

2^  G.M.T. 

Cor. 

58".53 
7  .1 

Ecius 
equa. 

I.  8""  3«                0.8 
6                7.1 

-8"^  9^                5.68 

Obs.  alt.  10°  49' 20" 
Cor.              +8  32 

Decl. 

0    40  36 
90    00  00 

5853 
40971 

T.  alt.      10°  57' 52" 

P.D. 

90°  40'  36" 

60)415.563" 

6'  55" 


T.  alt.          10°  58' 

T.  alt.  10°  58' 

Lat.             4')    58  sec      .16595 

Lat.     46    20  sec      .16086 

P.D.             90    41  cosec  .00003 

P.D.     90    41   cosec  .00003 

2)148    37 

2)147    59 

Half-sum    74    18  cos    9.43233 

73    59  cos  9.44078 

T.  alt.          10    58 

10    58 

Rem.  63°  20'  sine  9.95116  63°  01'  sine  9.94995 


2)19.54947  2)19.55162 

sine  9.77473  sine  9.77581 

9.77575 


6A  3^^ 


Double  Altitudes.  149 


Sept.        24"  19'^  07'"  44^  A.T.S.      Sept.     24"  19"  06">  r)3«  A.T.S. 
Equa.  -   8       9  -  08     09 


24  18 

59 

35 

M.T.S 

24  7 

6 

02 

M.T.G 

11 

53 

33 

15 

165 

13 

15 

8 

15 

178° 

23' 

15" 

E. 

24  18 

58 

44  M.T.S 

24  07 

06 

02  MT.C 

11 

52 

42 

15 

165 

13 

10 

30 

Long.  A,    178°  10'   30"  E. 
Long.  B, 

First  Line  of  Position,  N.  12^  E.  and  S.  12°  W.;  Sun's  True 
Bearing  S.  ?8°  E. 

Second  Observation. 


1894 

Sept.  24"  15'^ 

00 

^^  30= 

M.T.G. 

Equ 

a.  8™ 

3« 

0.8 

12 

15. 

Cor. 

Equa 

_Sm 

15^ 

12.0 

Decl 

0°  33 

41' 

S. 

58".53 

Obs. 

alt. 

26°  46' 

40' 

+  14 

38- 

s. 

" 

15. 

Cor. 
T.  a 

t. 

+  11 
26°  57' 

07 

0  48 

19 

29265 

47 

90  00 

00 

5853 

P.D. 

90°  48' 

19' 

60)877.95 

14'  38' 


T.  alt.        26°  58'  T.  alt  26°  58' 

Lat.  46    58    sec      .16595     Lat.     46    20  sec      .16086 

P.D.  90    48    cosec  .00004     P.D.     90    48  cosec  .00004 


2)164    44  2)164    06 

Half-sum^2    22  cos    9.12331  82    03  cos    9.14085 

T.  alt.        26    58  26    58 

Rem.  55°^'  sine  9.91547  55°  05'  sine  9.913&1 


2)19.20477  2)19.21556 

sine  9.60238  sine  9.60778 

9.60215  9.60761 

23  A  6«  17  A  5« 


150  TAYLOir.s  Modern  Navigation. 


Sept.   25"^  03" 
Equa. 

08"' 
-  8 

46« 
15 

A.T.S. 

M.T.S. 
M.T.G. 

E. 
W. 

25*^  03" 

11"^ 

-  8 

17^  A.T.S. 
15 

25  03 
24  15 

00 
00 

31 
30 

25  03 
25  15 

03 
00 

02  M.T.S. 
30  M.T.G. 

12 
15 

00 

01 

12 
15 

180 

180 
360 

02 

"30 

8 

38 
00 

32 

180 
360 

00 
00 

15 
00 

30 

Long.  D,  179° 

59' 

45" 

30  E. 
00 

Long.  C,  179°  21'    30"  W. 

Second  Line  of  Position,  N.  35°  W.  and  S.  35°  E.;  Sun's  True 
Bearing  S.  55°  W. 

Position  at  second  observation,  Lat.  47°  40'  N. ;  Long.  179° 
17'  E. 

LATITUDE  AND  LONGITUDE  BY  DOUBLE  ALTITUDES. 

This  section  of  the  book  is  one  of  the  most  important,  and  the 
application  of  these  modern  methods  enables  the  navigator  to  as- 
certain his  position  at  any  time  of  the  day  or  night,  whenever  celes- 
tial objects  are  visible. 

Those  methods  of  Double  Altitudes  whereby  the  Latitude  only  is 
found  are  obsolete,  and  may,  with  the  Lunars,  be  relegated  to  the 
dust-bin — in  fact,  they  are  so  very  much  out  of  date  that  mention 
of  them  at  all  is  questionable. 

It  is  a  great  wonder  that  the  methods  here  given  have  not  been 
more  generally  used  on  board  of  American  vessels,  for  when  we 
consider  that  the  latitude,  longitude,  and  sun's  true  azimuth  are 
all  found  with  one  Avorking,  the  great  benefit  to  be  derived  is 
enough  to  convince  the  most  skeptical  among  the  seafaring  class. 

The  working  of  a  Sumner  Method  is  simply  a  repetition  of  a 
common  chronometer  sight,  and  is  extremely  easy  to  learn,  but  it 
is  long,  tedious,  and  cumbersome,  because  the  approximate  posi- 
tions found  must  be  plotted  on  a  chart  of  a  sufficiently  large  scale 
before  the  desired  result  is  arrived  at;  still,  although  with  the  be- 
fore mentioned  defects,  it  is  of  the  greatest  utility  in  navigation,  for 
it  is  possible  to  navigate  a  vessel  with  this  method  alone,  without 
bavins:  resource  to  a  bitilude  observation. 


DouiJLE  Altitudes. 


151 


The  problem  illustrated  on  Chart  attached  to  this  section,  is 
an  extreme  case,  but  extreme  cases  are  always  best  for  illustra- 
tion, for  the  reason  that  the  subject  is  brought  more  forcibly  before 
the  student. 


Projection  o/^JuMN£R'5iiETHuu 


178  £ 


I78'£  '  I790E  '  180* 

In  practice  it  is  rarely  necessary  for  the  lines  of  position  and 
projection  to  be  extended  beyond  the  parallels  of  the  latitudes  used 
in  the  question  yet  it  may  occur  at  any  time,  and  if  it  should,  the 
problem  should  again  be  computed  by  selecting  a  latitude  beyond 


152  Taylor's  Moderx  Xavigation. 

the  point  of  intersection  of  the  lines,  rejecting  as  inaccurate  the 
previous  calculation. 

The  rule,  when  selecting  the  two  assumed  latitudes  wherewith  to 
compute  the  longitudes,  is  as  follows : 

Find  the  latitude  by  D.R.,  and  allow  about  20'  to  30'  on  each 
side  of  it  for  the  two  assumed  latitudes,  and  as  a  rule,  in  actual 
practice,  the  ship  will  always  be  found  between  these  parallels. 

It  should  be  remembered  that  latitude  gives  the  position  on  a 
parallel,  or  small  circle,  and  that  longitude  gives  the  position  on  a 
meridian,  or  groat  circle,  the  point  of  their  intersection  being  posi- 
tion of  place. 

It  is  always  possible  to  determine  the  ship's  place  on  a  part  of  a 
circle,  as  will  be  seen. 

If  the  declination  is  equal  to  the  latitude  of  the  place,  the  sun 
will  be  in  the  zenith  at  noon,  and  there  is  always  some  place  on 
the  earth's  surface  where  the  sun  is  vertical,  or  overhead,  and  there 
is  always  a  circle  on  this  earth,  surrounding  the  spot  where  the 
sun  is  vertical,  whereon  is  the  observer. 

Take  for  instance  a  flag-pole,  and  draw  a  circle,  say,  100  feet 
from  its  base.  Each  one  on  this  circle  having  the  same  height  of 
eye,  and  measuring  the  angle  between  its  summit  and  base,  would 
have  the  same  angle.  Advance  towards  the  pole,  and  the  angle 
increases ;  retreat  from  the  pole,  and  the  angle  decreases. 

This  is  true,  also,  in  regard  to  the  sun ;  for  of  any  number  of  ob- 
servers on  any  part  of  the  same  circle,  observing  the  sun  at  the 
same  instant,  each  and  every  one  would  have  the  same  altitude. 

If  these  circles  were  drawn  on  a  globe  they  would  be  true  circles. 
but  when  drawn  on  a  Mercator  chart  they  are  elliptical  figures, 
f^wing  to  the  apparent  increase  in  the  size  of  the  degrees  of  latitude, 
caused  by  representing  the  earth  as  a  plane  instead  of  as  a  sphere. 

In  actual  practice,  only  small  parts  of  circles  are  required,  but 
if  it  is  the  desire  of  the  student  to  obtain  the  whole  circle,  posi- 
tions must  be  computed  for  every  5°  of  latitude. 

In  the  case  of  the  sun,  the  first  observation  gives  only  a  position 
oil  one  circle,  and  although  a  knowledge  of  this  is  very  valuable,  still, 
it  does  not,  of  itself,  give  the  position  of  the  ship ;  therefore,  after 
waiting  about  one  and  a  half  hours,  so  as  to  allow  the  sun  to 
change  its  position,  or  to  become  vertical  to  some  other  place,  a 
second  observation  must  be  taken,  giving  another  circle,  whereon 
the  observer  is  also;  and  supposing  the  ship  not  to  have  changed 
her  position,  these  two  circles  would  be  seen  to  cross  each  other  twice, 


Double  Altitudes.  153 


if  plottiil  oil  a  chart,  but  at  widely  different  places  on  the  earth's 
surface;  and  as  cither  one  of  these  positions  will  give  the  ship's 
place,  it  is  hardly  necessary  to  state  how  easy  it  is  for  the  naviga- 
tor to  discern  the  proper  one,  his  D.R.  being  his  check,  and  we 
feel  assured  he  will  know  the  D.R.  inside  of  a  handful  of  degrees. 

If  the  ship  has  changed  her  position  between  the  two  observa- 
tions, it  will  be  necessary  for  the  first  circle,  or  line,  to  be  advanced 
according  to  the  direction  and  distance. 

This  matter  of  shifting  the  first  circle  along  is  the  greatest  draw- 
back to  the  method  being  applied  to  the  sun,  as  there  is  always  a 
considerable  element  of  doubt  in  correctly  estimating  the  true 
course  and  distance  sailed. 

But  here  the  stars  and  planets  come  to  the  rescue,  for  by  them 
it  becomes  possible  to  take  simultaneous  observations  of  two 
celestial  bodies  in  widely  different  directions,  namely,  one  body  ob- 
served to  the  East  and  the  other  body  to  the  West,  and  the  cir- 
cles, or  lines  as  they  will  hereafter  be  called,  when  plotted  on  the 
chart,  will  give  at  their  point  of  intersection  the  ship's  place,  en- 
tirely doing  away  with  D.R.  This  method  of  using  the  stars  may 
still  further  be  improved,  if  there  is  any  doubt  in  regard  to  the 
true  place  of  the  horizon,  by  observation  of  a  third  star  or  planet, 
and  plotting  this  line  on  the  chart.  All  doubt  will  then  b^'  entirely 
eliminated. 

All  lines  of  position  should  cut  each  other  at  any  angle  between 
60°  and  120°  to  insure  a  good  result;  if  the  angle  is  less  or  greater, 
the  intersection  of  the  lines  is  not  well  defined,  and  an  error 
amounting  to  several  miles  may  arise  in  the  desired  result. 

A  good  observer — and  remember,  it  is  the  "man  behind  the 
gun"  that  tells — ought  to  be  sure  of  the  observed  altitude  inside 
of  2',  provided  he  has  a  good  sextant,  well-silvered  glasses,  and  a 
good  star-telescope. 

It  will  be  seen,  therefore,  that  the  whole  object  of  the  problem 
is  to  locate  the  line  whereon  the  ship  will  be  at  the  time  of  taking 
an  observation.  By  the  rule  given  for  the  sun,  this  is  found  by 
working  the  sight  with  two  latitudes,  plotting  the  positions  found 
on  a  chart,  and  drawing  a  line  through  them;  but  by  reference  to 
the  rule  it  will  be  found  that  the  assertion  is  made  anent  the  sun's 
true  bearing  being  at  a  right  angle  to  the  line  of  position.  This  is 
illustrated  on  the  chart. 

jSTow,  if  the  sun's  true  bearing,  or  azimuth,  is  at  a  right  angle  to 
the  line  of  position,  it  stands  to  reason  that  the  line  of  position  is 


154  Taylor's  Moder^t  Navigation. 

at  a  right  angle  to  the  sun's  bearing.  This  is  a  very  valuable  point 
to  know;  for  if  it  is  possible  to  obtain  the  sun's  true-bearing,  it  is 
certainly  possible  also  to  obtain  the  line  of  position  from  it. 

Contained  in  every  chronometer  sight,  when  worked  out,  is  the 
A.T.S.,  latitude,  and  declination.  These  three  elements  given, 
with  the  assistance  of  American  Azimuth  Tables  the  sun's  true 
bearing  at  time  of  sight  may  be  found  by  inspection. 

Therefore,  work  the  sight  only  once  with  the  latitude  by  D.E., 
and  with  the  elements  as  before  mentioned  procure  the  sun's  true 
bearing,  and  either  add  or  subtract  90°.  The  result  will  be  the  line 
of  position,  as  correct  as  if  the  operation  had  been  performed 
iwice.  It  is  not  necessary  to  use  the  latitude  brought  forward  from 
the  first  sight  to  work  the  second,  but  it  is  more  correct. 

These  lines  of  position,  when  extended  and  drawn  on  a  chart, 
will  exhibit  the  bearing  of  the  land,  and  the  navigator  may  shape 
a  course  along  them  with  absolute  confidence  in  his  eventually  ar- 
riving at  the  point  indicated  by  the  line  dr.iwn.  provided  he  is 
ihoroughly  acquainted  with  the  errors  of  his  navigating  compass, 
and  provided,  as  soon  as  the  land  is  sighted,  he  takes  a  bearing  of 
some  prominent  object,  like,  for  instance,  a  mountain.  The  inter- 
section of  the  line  of  bearing  with  the  line  of  position  will  give  the 
ship's  place,  or  if  the  land  is  not  visible,  and  recourse  is  had  to  the 
lead,  the  ship's  place  may  be  determined  with  tolerable  accuracy, 
provided  soundings  are  taken  at  frequent  intervals  as  ship  ap- 
proaches the  land. 

In  a  preceding  part  of  this  book,  relating  to  the  modern  a.m. 
sight,  a  small  diagram  is  given,  proving  the  problem  by  graphically 
drawing  it.  it  will  be  noticed  that  the  sun's  true  azimuth  is  an 
important  element. 

An  ordinary  sight  worked  with  the  approximate  latitude  gives 
only  an  approximate  longitude,  yet  these  approximations  may  be 
utilized  by  striking  a  right  angle  to  the  sun's  bearing  at  time  of 
sight,  through  the  approximate  position,  giving  a  line  whereon  is 
the  ship,  but  on  what  part  is  not  known. 

With  the  course  and  distance  between  sight  and  noon  bring  posi- 
tion forward,  and  obtain  the  projected  line,  whereon  the  ship  will 
be  at  noon. 

At  noon  determine  the  latitude,  and  tbe  point  whore  it  cuts  the 
projected  line  will  be  the  position  at  noon,  provided  that  true 
course  and  distance  have  been  correctlv  estimated. 


DoiBLE  Altitudes.  155 


Sumner's  Method. 


tJ.ni  III  pics  fur  rraciice. 

1894,  August  15th,  8''  5'"  a.m.  at  ship,  the  sun's  true  alt.  was 
32°  G^  O0",-chronometer  showing  (S^  2°^  48*^  G.M.T.  and  after  sailing 
IS'.  11°  W.  true,  distance  35  miles,  a  second  observation  was  taken 
at  4'^  30™  P.M.,  chronometer  showing  2^  32°^  48^  G.M.T.,  the  sun's 
true  alt.  being  23°  37'  00" ;  ship's  position,  by  D.R.,  was  lat.  47°  7' 
N.  and  long.  147°  W.  at  time  of  first  sight;  assumed  lats.  to  work 
both  sights,  46°  50'  N.  and  47°  25'  N.  Eequired  the  ship's  posi- 
tion at  time  of  second  observation,  trend  of  lines  of  position,  and 
Sim's  true  azimuth  at  both  sights. 

Answers. — First  observation,  lat.  46°  50'  X.,  long.  147"  15'  \V.. 
lat.  47°  25'  X.,  long.  146°  59'  30"  W.;  second  observation,  lat.  46° 
50'  N.,  long.  147°  05'  30"  W.,  lat.  47°  25'  X.,  long.  147°  10'  30" 
W.  Ship's  position,  lat.  47°  50'  N.,  long.  147°  14'  W. ;  first 
line  of  position  N.  15°  E.  and  S.  15°  W.,  T.  az.  S.  75°  E. ;  second 
line  of  position,  N.  5°  W.  and  S.  5°  E.,  T.  az.  S.  85°  W. 

1894,  May  23d,  3^^  20°^  p.m.  at  ship;  the  chronometer  showed  1** 
20™  00^  G.M.T.,  when  the  sun's  true  alt.  was  40°  23'  00" ;  ship  then 
sailed  JST.  3°  W,  true,  distance  20  miles,  when  a  second  sight  was 
taken  at  5^^  30™  p.m.,  chronometer  showing  3"^  30™  00^  G.M.T. ; 
sun's  true  alt.  18°  21'  00";  ship's  position,  by  D.E.,  lat  46°  53'  N. 
and  long.  148°  W.,  assumed  lats.  to  work  both  sights  4(i°  38'  X. 
and  47°  8'  N.  Eequired  the  ship's  position  at  second  observation, 
lines  of  position,  and  sun's  true  azimuth. 

Answers.— First  observation,  lat.  46°  38'  X..  long.  148°  1!)'  W.. 
lat.  47°  8'  X.,  long  148°  30'  W. ;  second  observation,  lat.  46°  38' 
X.,  long.  148°  28'  30"  W.,  lat.  47°  8'  X.,  long.  148°  20'  W.  Ship's 
position,  lat.  47°  02'  30"  X.,  long.  148°  21'  W. ;  first  line  of  posi- 
tion, X.  13°  W.  and  S.  13°  E.,  T.  az.  S.  77°  W.;  second  line  of 
position,  X.  11°  E.  and  S.  11°  W.,  T.  az.  X.  79°  W. 

1894,  June  28th,  7"  30™  a.m.  at  ship;  a  chronometer  showed  5'^ 
38™  00«  M.G.T.,  when  the  sun's  obs.  alt.  was  34°  20'  53" ;  the  ship 
then  steamed  X.X.E.,  distance  18  miles,  when,  at  9''  40™  a.m.  on 
same  day,  a  chronometer  showed  7''  43™  00**  M.G.T.,  the  obs.  alt. 
of  sun's  L.L.  being  54°  46'  10";  no  instrumental  errors;  height  of 
eye  30  feet  at  both  sights.  The  ship  was  supposed  to  be,  by  D.E., 
in  lat.  46°  31'  X^.  long.  147°  40'  \A^  The  two  assumed  latitudes  to 
work  the  sights  are  16'  on  either  side,  namely,  46°  15'  X.  and  46° 


156  Taylor's  Modern  Navigation. 


47'  N.  Eeqiiired  the  position  of  the  vessel  at  time  of  second  sight. 
trend  of  lines  of  position,  and  sun's  true  bearing  or  azimuth. 

Answer.— First  observation,  lat.  46°  15'  N.,  long.  147°  30'  W.. 
lat.  46°  47'  N.,  long.  147°  29'  W.;  second  observation,  lat.  46°  15' 
N.,  long.  147°  57'  W.,  lat.  46°  47'  N.,  long.  147°  30'  W.  First 
line  of  position,  N.  2°  E.  and  S.  2°  W.,  sun's  true  bearing,  E.  2°  S. ; 
second  line  of  position,  N.  30°  E.  and  S.  30°  W.,  sun's  true  bearing 
S.  60°  E.;  position  of  ship,  lat  46°  36'  30"  N.^  long.  147°  39'  30" 
W.     (This  problem  is  worked  to  nearest  minutes  of  arc.) 

1894,  January  1st,  9**  30™  a.m.  at  ship ;  chronometer  showed  7'' 
36°!  28«  M.G.T.,  when  the  sun's  true  alt.  was  14°  03'  10" ;  ship 
then  steamed  E.N.E.  true,  distance  49  miles,  when  a  second  obser- 
vation was  taken  at  2^  p.m.,  chronometer  showing  12*^  02™  28' 
M.G.T.,  the  sun's  true  alt.  being  14°  21'  00";  ship's  position,  by 
D.E.,  lat.  46°  30'  N.,  long.  146°  20'  W.;  assumed  lats.  to  work 
sights  46°  12'  N.  and  46°  48'  N.  Kequired  the  ship's  position  at 
time  of  second  sight,  trend  of  lines  of  position,  and  sun's  true  bear- 
ing at  each  observation. 

Answer. — First  observation,  lat.  46°  12'  K.,  long.  147°  47'  W., 
lat.  46°  48'  N.,  long.  146°  23'  W.;  second  observation,  lat.  46°  12' 
N.,  long.  145°  44'  W.,  lat.  46°  48'  N.,  long.  147°  10'  W.  Ship's 
position,  lat.  46°  33'  N.,  long.  146°  33'  W.;  first  line  of  position,  N. 
58°  E.  and  S.  58°  W.,  sun's  true  bearing  S.  32°  E.;  second  line  of 
position  N.  59°  W.  and  S.  59°  E.,  sun's  true  bearing  S.  31°  W. 

JOHNSON'S  METHOD. 

We  have  pretty  well  thrashed  out  our  old  friend  Sumner;  so  it 
is  time  Ave  modified  him  somewhat.  This  may  be,  or  we  ought  to 
say  is,  done  by  substituting  the  method  called  "The  Double  Chro- 
nometer, or  Latitude  and  Longitude  in  Cloudy  Weather,"  by  Pro- 
fessor Johnson,  to  whom  all  honor  is  due  for  simplifying  many  mt :th- 
ods  now  in  every-day  use  on  board  of  ships  at  sea.  The  work  is  pub- 
lished in  pamphlet  form,  and  contains  but  one  table  that  we  wish 
to  use  here.     (See  end  of  book.) 

The  method  is  entirely  correct,  and  may  be  proven  liy  working 
Sumner's,  by  both  methods,  or  by  actual  test  when  at  sea. 

The  great  value  of  Johnson's  Method  lies  in  its  extreme  sim- 
plicity, brevity,  and  accuracy,  working  each  sight  only  once  (instead 
of  twice,  as  in  the  older  but  longer  methods),  with  a  very  short 
but  convenient  and  easy  calculation  by  division  and  multiplication 
of  decimals  at  the  latter  part;  but  in  this  part  of  the  problem  there 


Double  Altitudes.  157 


is  contained  an  item  not  found  in  any  other  question  in  naviga- 
tion, and  that  is,  when  it  is  finished  we  can  tell  if  we  are  right  or 
v/rong  in  the  working.  Do  not  misunderstand  this  assertion,  how- 
ever. When  it  is  said  we  can  tell  if  the  answer  is  right  or  wrong, 
what  is  really  meant  is,  we  can  tell  if  Mr.  Johnson's  method  is 
worked  correctly;  but  it  does  not  prove  that  the  observations  are 
correct.     This  is  very  important  for  the  navigator  to  understand. 

It  will  also  be  noticed  that  there  is  not  any  clumsy  plotting  to 
perform  on  a  chart,  the  same  as  in  Sumner's,  with  always  a 
considerable  element  of  doubt  in  determining  the  exact  point  of 
intersection  of  the  lines  drawn,  especially  when  they  do  not  cut 
distinctly;  and,  by  the  way,  it  is  quite  a  difficult  operation  to 
draw  a  line  straight  if  the  vessel  is  rolling  and  pitching  in  a  sea- 
wa}',  making  it  a  difficult  matter  to  keep  your  legs,  let  alone  the 
drawing  of  a  straight  line;  therefore  this  is  another  reason  why 
this  method  should  be  used  in  preference  to  old  Sumner's. 

And,  as  a  final  word,  we  wish  to  state  that  there  is  no  method 
in  existence  to-day  that  is  of  so  much  value  to  navigators  as 
'Johnson's,  therefore  the  seaman  may  use  it  with  the  most  absolute 
confidence,  and  any  errors  he  may  discover  are  his  own,  not  John- 
son's. 

We  speak  in  this  forcible  manner  because  there  is  a  tendency 
among  a  certain  class  of  seamen  to  decry  it  as  a  fancy  method, 
good  enough  for  boys  to  amuse  themselves  with,  but  not  for  us  old 
seamen,  who  crawled  through  the  hawse-pipes  and  worked  our- 
selves aft.    For  such  this  book  is  not  written. 

The  Rule. 

Take  two  ordinary  chronometer  observations,  with  an  interval 
between  of  about  an  hour  and  a  half  or  two  hours,  to  allow  the 
sun's  true  bearing  to  change  at  least  two  points.  The  reason  for 
allowing  the  sun  to  change  its  bearing  sufficiently  has  already  been 
explained  under  the  head  of  Sumner's.  Work  the  first  observation 
with  the  latitude  by  D.E.  the  ship  was  in  at  the  time  of  first  sight ; 
the  result  will  be  the  approximate  latitude  and  longitude  at  time 
of  first  sight;  bring  this  approximate  position  forward  to  time  of 
second  sight  by  using  the  true  course  and  distance  the  ship  sailed 
in  the  interval  between  sights;  the  result  will  now  be  the  approxi- 
mate position  of  ship  at  time  of  second  sight.  Call  the  longitude 
brought  forward  No.  1. 

Now  work  the  second  sight  with  the  latitude  brought  forward 


158  Taylor's  Moderx  Xavigatiox. 


from  the  first,  and  call  the  resulting  longitude  No.  2 ;  next  enter 
the  American  Azimuth  Tables  with  the  A.T.S.,  lat.,  and  decl. 
contained  in  each  sight,  and  take  out  the  sun's  true  bearing  for  each 
sight  and  mark  them  down;  then  mark  down  the- latitude  used  to 
work  the  second  sight  on  left  side  of  page,  as  seen  in  examples, 
then  No.  1  longitude  and  No.  3  longitude,  and  abreast  of  their  re- 
spective longitudes  mark  down  the  azimuths. 

Next  enter  Table  No.  2  in  Johnson's  Latitude  and  Longitude  in 
Cloudy  Weather,  and  with  the  nearest  degree  of  latitude  on  the  top 
and  the  nearest  degree  of  the  first  azimuth  on  the  side,  abreast,  and 
underneath  take  out  the  corresponding  number,  interpolating  if 
the  degrees  are  not  even,  and  mark  this  number  down  abreast  of 
the  first  azimuth  and  call  it  a;  then  do  the  same  with  the  second 
azimuth,  and  call  the  number  h ;  add  these  two  numbers,  a  and  h, 
if  the  bearings  have  different  names,  but  subtract  if  same  name. 

Find  the  difference  of  longitude  between  No.  1  and  No.  2  and 
divide  it  by  the  sum  or  difference  of  a  and  l.  The  result  will  be 
the  correction  for  the  latitude. 

Multiply  this  correction  for  the  latitude  by  a,  and  the  result  will 
be  the  correction  for  the  first  longitude. 

Multiply  the  same  correction  by  h,  and  the  result  will  be  the 
correction  for  the  second  longitude. 

Bule  to  Apply  the  Correction  for  the  Longitudes. 

First  Case. — When  the  bearings  are  in  the  same  or  opposite  quar- 
ters of  the  compass,  allow  both  corrections  to  the  East,  or  both  to 
the  West,  in  such  a  manner  as  to  make  the  two  longitudes  agree. 

Second  Case. — When  the  bearings  are  in  adjacent  quarters  of  the 
compass,  allow  the  easterly  longitude  towards  the  West,  and  the 
westerly  longitude  towards  the  East,  in  such  a  manner  as  to  make 
the  longitudes  agree. 

If  they  do  not  agree,  the  corrections  have  been  wrongly  applied, 
and  herein  there  is  a  safeguard  against  error,  peculiar  to  this 
method  only. 

To  Apply  the  Correction  to  tlic  Latitude. 

Under  No.  1  longitude  or  No.  2  longitude  mark  down  the  name 
of  the  azimuth  belonging  to  it,  and  under  it  again  mark  down  the 
opposite  bearing;  then  if  the  correction  to  the  longitude  was  W. 
tliat  letter  which  is  on  the  opposite  corner  to  W.  will  be  the  name 
of  the  correction  for  the  latitude. 


Double  Altitudes.  15!) 


Johnson's  Method. 

Example. — ISD-I,  January  1st.  7''  3()'"  a.  ii.  wln'ii  ship  was  in  !at. 
46°  30'  X.  and  long.  146°  30'  W.  by  D.K.,  the  following  sight 
was  taken :  Chronometer  showing  7"  36°^  38«  M.T.G. ;  sun's  true 
alt.  14°  03'  10".  The  ship  then  steamed  E.N.E.  true,  distance  49 
miles,  when  another  sight  was  taken  at  2*"  p.m.,  chronometer  show- 
ing 12^  02'°  28^  M.G.T. ;  sun's  true  alt.  14°  21'  00".  Find  latitude 
and  longitude  of  ship  at  time  of  second  obsirvation,  by  Johnson's 
Method. 

First  Observation. 


Jan.  1"  07^  36'"  28« 
Decl.  22°  59'  23"  S. 

M.T.G. 

12".7 
7  .6 

Equa.  3'"  53^      1.2 
9      7.6 

-1  36 

+  4'"  02«      72 

22  57  47  S. 
90  00  00 

762 
889 

84 
9.12 

P.D. 112°  57'  47" 

96.52 

T.  alt.  14°  03'  10" 

1'  36" 

T.  alt.        14°  03' 

Lat.  D.R.  46    30    sec      .16219 

P.D.         112    58    cosec  .03587 


2)173    31 


86  454  cos  8.75242 
14   3 


72°  42'  sine  9.97989 

2)"l8.93037 

sine  9.46518 
9.46511 

7A  V 


ATS   9''  44'"  A    ^r    "^ 

A.I.&.  J     -14     A.  M.    I  .^,    _^_^    j^.    ^^^o  j^ 

Lat.    47°  N.  y  1<^0 

'  T.  az.  S.     32°  E. 


Decl.  23°  S.  J 


ICO  Tayloij's  Modern  Xavigatiox. 


T.  CO.  E.  N.E.,  49;  D.  lat.  18.8;  Dep.  45.3. 

12^^  V 

9     44'"    16 


Dec.  31    21     44  15  A.T.S. 

+    4  02  equa. 

Dec.  31    21     48  17  M.T.8. 

Jan.     1     7     36  28  M.T.G. 


9^ 

48"" 

IP 

135 

12 

2 

45 

Approx.  post'n  first  sight,  lat.  46°  30' N.  Long.  147      2      45   W. 

19  N.  16 


Approx.post'n sec'nd  sight, lat. 46°  49'  N.            145°  56'    45"  W.  ( 1 ) 

Second  Observation. 

Jan.    1*^  12^  02™  28^  M.T.G.          Equa.  3"  53«  1.2 

14  12. 


Decl.         22°  59'  23"  S.       12.7  +  4"^  07^  14.4 

-  2  32  12. 


22    56  51   S.       254 

90    00  00  127     T.  alt.  14°  21'  00" 


P.D.         112°  56'  51"         152.4 


2  32 


T.  alt.  14°  21' 

Lat.  brought  forward       46    49      sec  .164/3 

P.D.  112    57      cosec  .03581 


)174   07 

87    03^    cos 
14    21 

8.71030 

72°  42'     sine 

9.97989 

2)18.89073 

9.44536 
44516 

20A  4"' 


Double  Altitudes.  IGI 


A.T.S.  2'.  lO-  P.  M.  ^                  ^g^. 

Lat.     47°  N.              y           N.  149     W. 

Decl.    23°  8.              J  ^-  -•  ^-    '''  ^^- 

Jan. 

I'l  02"  09'"  32«  A.T.S. 
+   4     07 

Jan. 

1    02    13     39    M.T.S. 

Jan. 

1    12    02     28    M.T.G. 

9    48     49 

135 

rox. 

Ion 

12    12     15 

App 

g.     147°  12'    15"    W.  at  second  sight     (2) 

Lat. 

46° 

49' 

N.              (1)     145°  57' W.            S.  32°E. 

a     2'.30 

16 

(2)     147    12  W.            S.  31°  W. 

N.                            1    15 

b     2.44 

46° 

33' 

4'.74 

60 

4.74)75.00(15'.82 
474 

2760 
2370 

3900 
3792 


1080 

948 

(1)  145°  57' W.       15'.82   (2)  147°  12' W.      15'.82 
36  W.       2.30  39  E.        2.44 


146°  33'  W.      47460       146°  33'  W.       6328 
3164  6328 

3164 

W.  38'.6008 


)'.3860 


N.  W.  N.  E. 

Johnson's  Method. 

Example.— 1S94,  June  28th,  at  ?•>  30'«  a.m.,  when  ship  was  in  lat. 
46°  31'  N.  and  long.  147°  40'  W.,  by  D.R.,  a  sight  was  taken,  when 
chronometer  showed  5^  38'"  00«  G.M.T.;  sun's  obs.  alt.  L.L.34° 

Taylor's  Mod.   Nav.   11. 


162  Taylor's  Modern  JSTavigation. 

20'  53";  and  after  steering  N.N.W.  18  miles  another  sight  was 
taken  at  9"^  40"^  a.m.,  chronometer  showing  '7^  43°^  00^  M.T.G.,  the 
obs.  alt.  sun's  L.L.  being  54°  46'  10".  Find  ship's  position  at  time 
of  second  observation,  by  Johnson's  Method. 

First  Observation. 
June  28*^  05^^  38'"  00^     M.T.G. 


Decl.             23°  17'  05"  N.                  7.2 
-  40                         5.6 

+  3           5.6 

+  3     02           2.80 

Cor.  Decl.    23    16  25     N.                432 
90    00  00                      360 

Obs.  alt.      34°  20'  53" 

P.  D.            66°  43'  35"                    40.32 

+     9   12 

T.  alt.         34°  30'  05" 

Alt.              34°  30' 

Lat.  D.  R.  46    31   sec     .16232  A.T.S.  7^  45'"  A.M.  )  T.az.  N.92°E. 

P.  D.           66    44  oosec  .03684  Lat.          47°  N.       [             180 

2)147    45                        Decl. 

Half-sum    73    52  cos  9.44385 
T.  alt.          34    30 

23°  N.        1  T.az.S.88°E. 

Kem.           39°  22' sine  9.80228 

2)19.44529 


sine9.72264 

W 

2« 

9.72259 

7    45'" 

04 

A.M. 

5A2« 

27  19    45 

02 

A.T.S. 

'.  CO.  N.  N.W.  18;  D.  lat.  16.6;  Dep.  6.9 

+   3 

02 

equa. 

27  19    48 

04 

IVLT.S. 

28  05    38 

00 

M.T.G. 

9    49 

56 

15 

135 

12    15 

14 

Approx.  position  Lat.  46°  31'  N long.   147    29  00    W. 

17   N.                                10  00    W. 

Approx.  position  at  j  -^^r^, 147°  39'  00"  W. 

second  sight  .  .     ^ 


Double  Altitudes.  16S 


Second  Observation. 


June      28"  07'^  43"'  00«  M.T.G. 

Decl.         23°  17'  05"  N.  7.2         Equa.  2"»  59"  .5 

55  7.7  4  7.7 


Cor.  decl.  23    16   10    N.  504  +3     03  3.85 

90    00  00  504 


P.D.         66°  43'  50"  55.44  Obs.  alt.   54°  46'  10" 

+  10  00 


T.  alt.      54°  56'  10' 


T.  alt.  54°  56' 

Lat.  brought  forward  46    48  sec      .16460 

P.D. 


66 

44 

cosec  .03684 

)168 

28 

84 

14 

cos    9.00207 

54 

56 

29° 

18' 

sine  9.68965 

2)18.89316 

9.44658 
.44646 

12 A  2^ 


12^ 

2^ 

A.T.S.  9*'  50™ 

)  T.  az.  N.  120°  E. 

9    50"° 

08 

Lat.    47°  N. 
Decl.  23°  N. 

[                  180 

A.T.S. 

27    21    .50 

06 

)  T.  az.  S.    60°  E. 

Equa. 

+  3 

03 

M.T.S. 

27   21    53 

09 

M.T.G. 

28   07    43 

9    49 
15 

135 
12    15 
12 

00 
51 

45 

Long.  (2)  147°  27' 

45"  W. 

164  Taylor's  Modekx  Xavigatiox. 


Lat.brt.fwd.46°4'8'N.    (1)  Long.  147°  39' W.      S.  88°  E.     o  0'.05 
9  S.     (2)  Long.  147    28  W.      ^.  BO   E.     b  \  .21 

Lat.  in,  46°37'N.  1.16)11.00(9'.48  IMG 

10.44 

560 
464 


928 


39'  W.        9'.48     Long.  (2)  147°  28'  W.       h  9'.48 
a  .05  11  W.  1  .21 


.4740  147°  39'  W.  948 

S.         E.  1896 


948 
11'.4708 


N.      W. 

Ansiver—Lat.  46°  37'  N.;  Long.  147°  39'  W. 

Examples  fur  Fvactifc. 

1894,  August  15th,  8^^  05-^  a.m.,  when  ship  was  in  lat.  47°  7'  N. 
and  long.  147°  W.  by  D.E.,  the  sun's  true  alt.  was  32°  6'  00", 
chronometer  showing  &"  2"^  48^  G.M.T, ;  the  ship  then  steamed  X. 
11°  W.  true,  distance  35  miles,  when  a  second  observation  was 
taken  at  4'>  30°^p.m.,  chronometer  showing  2*'  32"^  48^  G.M.T.,  sun? 
true  alt.  being  23°  37'  00".  Find  ship's  position  at  time  of  second 
sight,  by  Johnson's  Method. 

Answers. — First  approximate  position,  lat.  47°  41'  N.  and  long. 
147°  17'  W.;  same  brought  forward,  lat.  47°  41'  N.  and  long.  147° 
17'  W.  Second  approximate  position,  lat.  47°  41'  N.  and  long. 
147°  13'  W.  1st  az.  S.  65°  E.;  2d  az.  S.  85°  W.,  a  0.32.,  h  0.12; 
diff.  0.44;  difP.  of  long,  4';  corr.  for  lat.  9'.09;  corr.  for  1st  long. 
3'  E.;  corr.  for  2d  long.  1'  W.  Ship's  position  lat.  47°  50'  N.  and 
long.  147°  14'  W. 

1894,  May  23d,  3*^  20-"  r.M.,  when  the  ship  was  in  lat.  4G°  53'  X 
and  long.  148°  W.  by  D.R.,  a  chronometer  showed  l'^  20'"  00* 
G.M.T.,  when  the  sun's  true  alt.  was  40°  23'  00" ;  ship  then  steamed 
N.  3°  W.  true,  distance  20  miles,  when  a  second  observation,  at 
5^  30'"  P.M.,  was  taken,  chronometer  showing  3''  30'"  00^  G.M.T., 
gun's  true  alt.  18°  21'  00".  Find  ship's  position  at  time  of  sec- 
ond sight,  by  Johnson's  Method. 


The  Stars.  165 


Answers. — First  approximate  position,  lat.  4()°  53'  N".  and  long. 
148°  24'  W.;  same  brought  forward,  lat.  47°  13'  N.  and  long  148° 
25'  W.  Second  approximate  position,  lat.  47°  13'  N.  and  long. 
148°  18'  W.;  1st  az.  S.  77°  W.;  2d  az.  N.  79°  W.;  a  0.33;  h  0.28; 
corr.  for  lat.  11'  S.;  corr.  for  1st  long.  4'  E.;  corr.  for  2d  long. 
3'  W.;  ship's  position,  lat.  47°  2'  N.  and  long.  148°  21'  W. 

THE  STARS,  AND  HOW  TO  FIND  THEM. 

It  is  absolutely  necessary,  before  proceeding,  for  the  student  to 
supply  himself  with  a  set  of  good  star-charts.  These  the  United 
States  government  has  published  at  the  ridiculously  small  sum  of 
ten  cents  each.  There  being  only  two  charts,  the  ambitious  naviga- 
tor can  fit  himself  out  for  exactly  twenty  cents.  We  think,  however, 
that  it  would  be  much  better  if  the  Hydrographic  Office  charged 
more,  for  then  the  agents  would  try  to  sell  them,  instead  of  keep- 
ing them  in  the  background  and  showing  to  the  purchaser  only 
those  whereon  a  decent  profit  is  made. 

There  are  other  very  excellent  star-maps.  The  very  best  of  these, 
from  the  writer's  point  of  view,  are  published  by  Prof.  J.  M.  Kelly 
of  San  Francisco,  California.  These  comprise  a  set  of  seven  maps, 
one  being  a  map  of  the  comparative  sizes  of  the  sun,  the  planets 
and  their  satellites. 

We  wish,  also,  to  direct  the  student's  attention  to  a  most  excel- 
lent work,  entitled  Popular  Astronomy,  by  Professor  Simon  Xew- 
comb,  who  was  superintendent  of  the  American  Nautical  Almanac 
at  the  time  of  its  publication. 

It  is  hardly  necessary  to  state  that  stars  are  seen  only  at  night, 
for  the  reason  that,  the  sun's  light  being  so  strong,  they  are  ob- 
scured; therefore  the  stars  we  see  are  those  that  occupy  that  half 
of  the  celestial  sphere  opposite  to  that  occupied  by  the  sun.  As 
the  earth  moves  in  its  path  around  the  sun,  we  are  on  different 
sides  at  different  seasons;  and  if  it  were  possible  to  see  beyond 
him,  we  should  see  the  stars  change.  But  what  is  not  possible  dur- 
ing the  day  is  possible  at  night;  and  if  the  stars  behind  the  sun 
change,  those  in  the  opposite  part  of  the  celestial  sphere  must  also 
change. 

It  is  therefore  very  evident  that  the  earth,  in  its  annual  revolu- 
tion around  the  sun,  will  have  each  part  of  the  visible  celestial 
sphere  in  turn  exposed  to  view.  This,  however,  will  depend  en- 
tirely on  the  observer's  latitude  and  the  declinations  of  the  stars ; 
the  rule  being  that  stars  whose  declinations  are  greater  than  the 


166  Taylor's  Moderx  Xayigation. 

colatitiide,  when  latitude  and  dfclination  are  of  different  names, 
will  not  rise  above  the  horizon. 

The  total  number  of  stars  visible  to  the  naked  eye  is  about  five 
thousand,  but  this  depends  a  great  deal  on  the  atmosphere  and  the 
eye's  training. 

Herschel  and  Struve  estimated  that  about  twenty  million  were 
visible  with  Herschel's  twenty-foot  telescope,  but  since  their  time 
telescopes  have  been  much  improved,  and  although  no  reliable 
estimate  has  been  made  since  then,  yet  the  number  visible  with 
the  present  facilities  must  be  about  double  Herschel  and  Struve's 
estimate. 

Stars  are  classified  according  to  their  brightness,  which  is 
termed  magnitude,  and  this  is  indicated  by  numbers;  for  instance, 
Sirius,  Altair.  and  Aldebaran  are  of  the  first  magnitude,  but  the 
Pole-star  is  only  of  the  second  magnitude.  Sometimes  a  decimal 
is  used  for  greater  accuracy,  and  is  expressed  thus,  1.2,  meaning  a 
magnitude  between  the  first  and  second. 

For  the  purposes  of  navigation,  there  are  catalogued,  in  the 
American  Nautical  Almanac,  150  stars,  19  being  of  the  first  mag- 
nitude, 50  of  the  second,  72  of  the  third,  and  9  of  the  fourth. 
Stars  of  lesser  magnitude  have  no  practical  use  in  navigation. 
Stars  visible  with  the  largest  and  best  telescopes  are  of  about  the 
sixteenth  magnitude,  but  the  system  of  measurement  in  use  at  the 
present  time  is  far  from  being  perfect.  The  earliest  catalogue 
known  is  found  in  the  Almagest  of  Ptolemy,  supposed  to  be  that 
of  Hipparchus.  dating  as  far  back  as  150  years  before  the  Chris- 
tian era,  and  with  it  we  find  that  the  position  of  the  stars  then  and 
now  is  practically  the  same.  There  is  a  small  discrepancy,  but  the 
best  astronomers  attribute  it  mostly  to  errors  in  cataloguing. 

Stars  were  divided  into  groups,  or  constellations,  by  the  an- 
cients, but  it  is  very  hard  to  discern  any  likeness  to  the  men, 
women,  animals,  and  reptiles  whose  names  they  applied  to  the 
groups,  although  on  many  school  celestial  globes,  and  in  books, 
these  names  are  still  given,  the  system  being  popular  among  the 
people,  but  on  modern  maps  it  is  entirely  disregarded. 

The  matter  of  naming  the  stars  is  one  of  considerable  difliculty. 
The  ancients,  in  naming  the  groups,  applied  to  them  such  names 
as  the  Great  Bear  (Ursa  Major),  Little  Bear  (Ursa  Minor),  Grea* 
Dog  (Canis  Major),  Little  Dog  (Canis  Minor),  etc.  The  Arabs 
adopted  the  plan  of  giving  special  names,  or  borrowed  names  from 
the  Greeks. 


The  Stars.  167 


The  modern  luetliod  of  naming  the  stars  is  that  of  using  the  let- 
ters of  the  Greek  alphabet,  after  which  are  given  the  names  of  the 
constellations,  the  CI  reek  being  the  Christian  name,  and  the  con- 
stellation appellation  the  family  name,  and  when  the  Greek  alpha- 
bet is  exhausted,  recourse  is  had  to  the  Latin  alphabet  with  a  sys- 
tem of  numbers. 

The  student,  when  learning  the  stars,  should,  with  the  assist- 
ance of  the  star-maps,  before  mentioned,  endeavor  to  locate  some 
of  the  most  prominent.  In  the  northern  hemisphere  the  first  one 
to  locate  is  Ursa  Major,  popularly  known  as  the  Great  Bear,  or 
Dipper.  This  group  consists  of  seven  stars;  three,  almost  in  a  line, 
are  called  the  Bear's  tail,  the  other  four  forming  the  body ;  the  two 
in  the  shoulder  and  fore  leg  are  called  the  pointers  (on  the  map 
they  are  marked  with  an  arrow  pointing  towards  the  Pole-star), 
and  are  famous  for  their  usefulness  in  assisting  the  observer  to  find 
the  Pole-star,  or  Polaris.  This  useful  star  is  nearly  always  above  the 
liorizon  in  north  latitude,  and  is  situated  at  the  end  of  the  tail  of 
the  Little  Bear,  or  Ursa  Minor,  a  group  which  is  almost  an  exact 
counterpart  of  Ursa  Major,  only  much  smaller  and  not  so  bright. 

After  locating  these  two  groups,  the  identification  of  the  others 
is  easy  if  the  following  instructions  are  carried  out : 

Glue  the  map  on  a  smooth  board  and  glaze  it  so  that  it  may  be 
washed  if  it  gets  soiled  by  handling;  have  a  bull's-eye  lantern 
handy,  with  some  one  standing  by  to  throw  a  light  on  the  chart,  as 
it  will  take  both  hands  to  hold  it. 

Face  the  North,  hold  the  clu^rt  above  your  head,  with  the  con- 
fctellations  of  Ursa  Major  and  Ursa  Minor  in  same  position  as  seen 
on  the  sky  itself;  you  will  then  see  on  the  cliart  the  various  groups 
v.'ith  their  names  attached  to  them. 

Now,  suppose  Ursa  Major  to  be  to  the  left  of  the  pole,  but  a  little 
below  it;  then  about  the  same  distance  to  the  right  of  the  pole 
will  be  seen  Cassiopeia,  the  throned  woman,  which  is  easily  recog- 
nized by  the  four  comparatively  bright  stars  in  a  broken  line  at 
right  angles  to  one  another. 

Next  in  order  comes  Perseus,  a  brilliant  constellation,  situated 
in  the  Milky  Way,  and  a  little  farther  from  the  pole  than  Cassio- 
peia. It  may  be  recognized  by  a  string  of  good  stars  stretching 
along  the  Milky  Way.    It  contains  the  variable  star  Algol. 

It  will  now  bo  necessarv  to  locate  another  constellation ;  and  the 


ITiS  Taylor's  Modern  Navigation. 


observer  should  bear  in  mind  that  it  depends  on  the  time  of  year  and 
the  time  of  night  when  certain  stars  can  be  seen. 

We  will  therefore  next  select  the  beautiful  constellation  of 
Orion.  This  should  be  easy,  because  of  the  brilliancy  and  peculiar 
grouping  of  the  stars,  there  being  three  of  the  second  magnitude 
close  together  and  in  a  straight  line,  called  the  Belt  of  Orion;  four 
other  good  stars  will  be  found — two  above  and  two  below — the  two 
upper  ones  representing  the  shoulders  of  Orion,  and  the  lower  ones 
the  knees.    All  of  these  stars  may  be  used  in  navigation. 

A  line  drawn  through  the  Belt  of  Orion  will  pass  close  to  the 
star  Sirius,  the  brightest  star  in  the  heavens,  situated  in  the  con- 
stellation of  Canis  Major,  or  Great  Dog. 

A  line  drawn  from  Sirius  through  the  shoulders  of  Orion  will 
pass  close  to  Aldebaran,  commonly  called  by  seamen  the  Bull's-eye. 
It  is  easily  recognized,  for  it  is  the  brightest  of  tive  stars  forming 
the  letter  V. 

A  line  drawn  from  Aldebaran  to  Ursa  Major,  passing  through 
Taurus,  will  pass  close  to  Capella. 

Numerous  other  examples  of  finding  the  stars  could  be  given,  but 
we  think  the  above  will  be  sufficient  to  show  how  to  use  the  map. 
It  will  be  noticed,  however,  that  there  are  many  stars  on  the  map 
with  no  name  attached.  We  will  therefore  show  how  the  names  of 
those  stars  used  in  navigation  may  be  marked  on  the  map  for  easy 
reference. 

On  the  outer  edge  of  the  map  is  marked  the  right  ascension  in 
Eoman  numerals.  The  inner  circles  represent  the  declination  for 
every  ten  degrees.  By  inspecting  these  circles  it  will  be  noticed 
that  stars  having  declinations  not  exceeding  30°  S.  are  given,  as 
well  as  all  those  having  North  declinations. 

Now  open  the  Nautical  Almanac  under  the  head  of  fixed  stars 
and  take  the  first  one,  with  its  right  ascension  and  declination,  lay 
a  straight-edge  over  the  pole  and  the  right  ascension  on  edge  of 
map,  measure  along  the  straight-edge  the  declination  and  see 
what  star  corresponds  to  them,  and  if  the  star  is  not  marked, 
write  in  the  Nautical  Almanac  name.  This  Avill  make  the  chart 
more  valuable  to  the  navigator.  We  advise  this  to  l)e  done  with 
all  the  stars  on  the  maps  before  mounting  thcMu  on  tlu'  hoards  for 
practical  use.  And,  by  the  way,  the  method  of  finding  the  stars  in 
the  southern  hemisphere  is  the  same  as  that  for  the  northern,  with 


Double  Altitudes.  109 


the  exception  that  the  observer  must  face  to  the  South  instead  of 
the  North,  locating  first  the  Southern  Cross,  and  from  it  striking 
lines  and  angles  to  locate  other  constellations.  We  hope  that  these 
instructions  will  be  of  assistance  to  the  navigator,  for  many,  we 
feel  assured,  would  use  star-observations  to  locate  the  ship's  posi- 
tion if  they  could  only  learn  the  stars. 

Following  this  article  are  given  the  simultaneous  observations 
of  stars  previously  mentioned  in  the  explanations  of  Summer's  and 
Johnson's  methods,  and  the  navigator  is  advised  to  try  them,  but 
he  must  not  imagine  he  will  be  successful  at  first,  as  it  takes  con- 
siderable practice  to  measure  the  altitude  correctly.  But  practice 
makes  perfect. 

If  at  any  time  the  observer  sees  what  he  considers  to  be  a  star 
in  or  near  a  constellation,  but  which  is  not  found  on  the  star-map, 
this  will  be  found  to  be  a  planet,  and  not  a  star. 

To  find  out  what  planet  it  is,  enter  the  Nautical  Almanac  under 
a  planet's  name,  and  abreast  of  the  date  take  out  its  right  ascen- 
sion and  declination  and  plot  them  on  the  star-map;  if  this  gives 
the  same  position  as  that  of  the  one  observed,  you  have  the  planet's 
name ;  if  not,  try  another  one. 

It  is  a  very  good  plan  for  the  navigator  to  have  pins  with  the 
names  of  the  planets  attached,  and  from  day  to  day,  as  the  planets 
change  their  positions,  he  should  place  the  pins  according  to  their 
right  ascension  and  declination.  The  navigator  can  then  always 
tell  a  planet  at  sight,  with  the  assistance  of  the  constellations  in 
its  vicinity. 


LATITUDE  AND  LONGITUDE  BY  DOUBLE  ALTITUDE 
OF  STARS. 

1894,  June  14th,  about  midnight,  when  ship  was  in  lat.  26°  51' 
S.  and  long.  44°  20'  W.  by  D.R.,  the  following  nearly  simultane- 
ous observations  were  taken : 

T.  alt  of  fd  Aquarii  36°  39',  bearing  E.;  chron.  3»'  23"^  10^  G.M.T. 
T.  alt.  of  Spica  22°  AiV,  bearing  W.;  chron.  3"  24""  00^  G.M.T. 
Required  ship's  position  at  tinae  of  observation. 


i:o 


Taylor's  Modern  Navigation. 


/3  Aquarii. 
June  W  15*^  23"  10^  M.T.G. 
Decl.    6°  02'  15"  S.         R.A.     21'^  25'"  59» 
90    00  00 

P.D.  83°  57'  45"  T.  alt.  36°  39'  00" 

Spica. 
June  14''  15'^  24°^  00«  G.M.T. 
Decl.  10°  36'  29"  S.         R.A.     13'^  19™  36* 
90    00  00 

P.D.  79°  23'  31"  T.  alt.    22°  46'   00" 

Sid.  T.  mean  noon,  5'^  31™  05^ 
2  32 


T.  alt.      36°  39' 
Lat.          26    51 
P.D.         83    58 

Red.  sid.  time, 

sec        .04954 
cosec    .00241 

cos     9.44733 
sine    9.78030 

5'^ 

T.  a 
Lat. 
P.D, 

33™ 

It. 

2) 

37« 

22°  46' 
26    51 
79    24 

sec  .04954 
cosec  .00748 

2)147    28 

129    01 

73    44 
36    39 

64    30 

22    46 

cos    9.63398 

37°  05' 

41°  44' 

sine  9.82326 

2)19.27958 
sine    9.63979 

2)19.51426 
sine  9.75713 

20^  33™  03« 
+  21  25  59  R.A. 

17  59  02  R.A.  of  Mer. 
-  5  33  37  red.  sid.  T. 


14 

12 

25 

25   M.T.S, 

14 

15 

23 

10   M.T.G 

2 

57 

45 

15 

30 

14 

15 

11 

15 

Long.  44°  26'  15"  W. 


04"^  38™  56« 
+  13  19  36  R.A. 


17  58  32  R.A.  of  Mer. 
-  5  33  37  red.  sid.  T. 


14  12  24  55  M.T.S. 
14  15  24  00  M.T.G. 


2 

59 

05 

15 

30 

14 

45 

1 

15 

Long.  44°  46'  15"  W. 


Double  Altitudes.  171 


Lat.  26°  51'  S.    (1) 

44°  26'  W. 

T 

.  az.  N.  77° 

E. 

=  a  0'.25 

1  27  N.    (2) 

44  46  W. 
0T23720.00(: 

87 

T, 

.  az.  S.  88° 

W. 

=  6  0.02 

Lat.  25°  24'  S. 

0'.23 

184 

160 

161 

(1)  44°  26'  W. 

87. 

(2) 

44°  46'  W. 

87. 

22  W. 

0.25 

2  W. 

0.02 





. — 



Long.  44°  48'  AV. 

435 

44°  48'  W. 

1.74 

N.    E. 

174 

S. 

,W. 

S.    W. 

2T.75 

N. 

E. 

Answer.— Lat  25°  24'  S. ;  lonoj.  44°  48'  W. 


Examples  for  Practice. 

1894,  January  2;th,  at  1^  30°^  a.^l,  when  ship  was  in  lat.  36°  26' 
S.  and  long.  50°  07'  W.,  by  D.R.,  the  following  nearly  simultaneous 
observations   were  taken : 

Arcturus  T.  alt.  9°  21',  bearing  E.;  chron.  0^  0'"  0^      G.  M.  T. 
a  Orionis  T.  alt.  14°  44'  bearing  W';  chron.  5'^  1'"  30^    G.  M.  T. 

Required  the  ship's  position  at  time  of  observation,  by  'Johnson's 
Method,  and  prove  same  by  chart. 

Ansivers.^Long.  by  Arcturus  51°  7'  15"  W.;  T.  az.  N.  57°  E. 
Long,  by  a  Orionis  49°  56'  W.;        T.  az.  N.  69°  W. 
Correction  for  lat.  56'  S.;  ship's  position  lat.  37°  22'  S.;  long. 
50°  22'  W. 

1894,  May  20tli,  p.m.,  when  ship  was  in  lat.  25°  15'  i!^.  and  long. 
152°  W  by  D.E.,  the  following  nearly  simultaneous  observations 
were  taken : 

Arcturus  T.  alt.  51°  10',  bearing  E.;  chron.  5"  35""  10s. 
Procyon  T.  alt.  31°  17',  bearing  W.,  chron.  5"  35'"  40^ 


172 


Taylor's  Modekx  Xavigation. 


Kequired  the   ship's   position   at  time   of   sight,   by   Johnson's 
Method,  and  prove  same  by  chart. 

Armoers.—Long,  by  Arcturus  151°  42'  30"  W.;  T.  az.  N.  89°  E. 
Long,  by  Procyon   151°  25'  45"  W.;  T.  az.  S.  81°W. 
Correction    for   lat.    106'   N.;    Ship's  position  lat.  27°  01' N.; 
long.  151°  44'  W. 


Illustration  of  Double  ^tar.  0b3ER,vation5 

LOOKING  50UTH 
4yw  AA"^  AS^W  46V 


'i'^ot 

1         1         1         1         1 

1       1       1       1       1 

1 1 1 1 1 

27  -i- 

^  Aquarii       :^ 

^          4 
A        r 

\           3 

\      - 

L 

_rA^5P'^*      - 

?fi'^ 

- 

7^°i 

- 

V 

5hip>  R}st( 

\ 

- 

1       1       I      1       1 

1      1      1      1      1 

1         1         1         1          1 

27*^ 


LINE5  OF  POSITION-  FOUND  BY  STR.IKING   A 
R^IGHT  angle:  to  JTAR'3    AZIMUTH 


26* 


25* 


DIVISION  YIII. 

DEVIATION  OF  THE  COMPASS. 

An  Amplitude  is  the  bearing  of  the  sun  when  it  is  just  rising 
above  the  horizon,  or  as  it  touches  the  horizon  when  setting. 

To  Take  the  Observation. — As  the  sun's  lower  limb  touches  the 
horizon,  take  a  bearing  of  it  by  the  ship's  compass,  and  note  the  ap- 
parent time  at  ship;  also,  note  the  direction  of  the  ship's  head  at 
the  time  when  the  bearing  was  taken,  because  the  deviation  found 
will  be  for  that  point  only. 

EULE. 

If  the  time  at  ship  is  a.m.,  add  12  to  the  hours  and  put  the  ship's 
date  one  day  back;  if  the  time  is  p.m.,  put  the  ship's  date,  hours, 
minutes,  and  seconds  down  as  they  stand;  convert  the  longitude 
into  time,  and  add  it  to  the  ship's  time  if  the  longitude  is  West,  but 
subtract  if  East;  the  result  will  be  the  Greenwich  apparent  time 
(G.A.T.);  now  take  out  of  the  Xautical  Almanac  the  sun's-  de- 
clination and  difference  for  one  hour,  abreast  of  the  Greenwich 
date,  and  correct  it  the  same  as  it  is  done  in  the  meridian  altitude, 
problem;  mark  down  the  latitude,  and  under  it  put  the  correct  de- 
clination to  the  nearest  minute;  take  out  of  Table  44  the  secant  of 
the  latitude  and  the  sine  of  the  corrected  declination;  add  these 
logs. ;  the  sum,  rejecting  the  tens  in  the  index,  -will  be  the  sine  of 
the  true  amplitude  (T.  amp.).  Table  44. 

If  you  read  sine  from  the  top,  you  must  read  the  degrees  at  the 
top  and  the  minutes  on  the  left ;  if  you  read  sine  from  the  bottom, 
read  the  degrees  at  the  bottom  and  the  minutes  on  the  right. 

To  Name  the  True  Amplitude. — If  the  time  is  a.m.,  name  it 
East;  if  p.m.,  name  it  West;  and  towards  the  North  or  South  ac- 
cording as  the  declination  is  North  or  South.  Under  the  T.  amp. 
put  the  obs,  amp.,  adding  if  of  different  names,  subtracting  if  same 
name.     The  result  will  be  the  error  of  the  compass. 

To  Name  the  Error. — Let  the  student  imagine  himself  standing 
in  the  center  of  the  compass-card  and  looking  towards  the  bearings ; 
then  if  the  T.  amp.  is  to  the  right  of  the  obs.  amp.,  the  error  is 
East;  if  to  the  left,  the  error  is  West.  Under  the  error  put  the 
variation,  adding  if  of  different  names,  subtracting  if  same  name. 
The  result  will  be  the  deviation. 


174 


Taylor's  Modern  Navigation. 


To  Name  the  Deviatimi. — Stand  in  the  center  of  the  compass 
and  look  towards  the  North  point ;  then  if  the  error  is  to  the  right 
of  the  variation,  the  deviation  is  East;  if  to  the  left,  the  deviation 
is  West. 


Example.— I'i'd^,  January  14th,  at  1^  43'"  a.m.,  A.T.S.,  in  lat. 
49°  50'  N.  and  long.  127°  31'  W. ;  sun's  obs.  amp.  was  E.XS.; 
variation  22°  10'  E.  Kequired  the  deviation  of  the  compass  for  the 
position  of  the  ship's  head  at  time  of  observation. 


Jan]  [14'' 07^  43" 
12 


00« 


18   19   43 

8   30 


00 
04 


G.A.T.  14'^  04^  13"^^  04« 


Long.  127°  31'  W 
4 


60  )  5  10  04 


8^  30'"  04* 


Decl.  21°  15'  25"  S. 

1  53 

Cor.  Decl.  21°  13' 32"  S. 


26".93 
4  .  2 

53  86 
1077  2 

60  )  113.1  06 

1'  53" 


Sec.  of  lat.        49°  50'  N.  10.19043 
Sine  cor.  Decl.  21°  14'  S.     9.55891 


Sine  9.74934 


T.  amp.  E.      34°  10'  S. 
Obs.  amp.  E.  11    15   S. 

Error 
Var. 

Dev.  00°  45'  E. 


22   55  E. 
22   10  E. 


Deviation. 


175 


Example.— lS9i,  May  1st  at  6'^  36'"  p.  m.,  A.T.S.  in  lat.  31°  20' 
N.  and  long.  42°  17'  W.;  sun's  obs.  amp.  was  W.1/4S.;  variation 
27°  51'  E.  Reqiiired  the  deviation  of  the  compass  for  the  position 
of  the  ship's  head  at  time  of  observation. 


May 


G.A.T 


1'^  06"  3()' 
2   49 


00« 
08 


1*^  09"  25'"  08^^ 


Long. 


42^ 

17' 
4 

W. 

60) 

169 

08 

2" 

49m 

08^ 

45".24 

Decl.          15°  09'  29" 

N. 

9.  4 

7   05 

18096 

Cor.  decl.  15°  16'  34' 

N. 

40716 

60)425.256 

W 

7' 05' 


o^*- 


Sec.  of  lat         31°  20'     10.06846 
Sine  cor.  decl.  15°  17'       9.42093 

Sine  9.48939 


T.  amp.      W. 

17°  58'  N 

Obs.  amp.  W. 

2    49  S. 

Error 

20    47   E 

Var. 

27    41   E. 

Dev. 

70    4'w 

A    SHORT,    PRACTICAL,    AND    CORRECT    METHOD    OF 

FINDING  THE  DEVIATION  BY  AN  AMPLITUDE, 

USING  TABLE  39,  BOWDITCH  EPITOME. 

In  actual  practice  it  is  not  necessary  to  work  the  problem  of 
amplitudes  by  so  lengthy  a  method  as  that  given  in  the  preceding 
rule,  for  the  reason  that  it  is  impossible  to  observe  the  bearing 
nearer  than  a  half-degree  with  the  instruments  used  for  the  purpose 
on  board  ships. 

The  method  here  given  requires  only  the  latitude  to  the  nearest 
degree,  and  the  declination  to  tlie  nearest  half -degree,  taken  at 
sight  from  the  Nautical  Almanac  abreast  of  the  date. 


176 


Taylor's  Modern  Navigation. 


With  these  elements  enter  Table  39  of  Bowditch,  and  under  the 
declinations,  and  abreast  of  the  latitude,  will  be  found  the  sun's 
true  amplitude,  in  degrees  and  tenths;  convert  the  tenths  into 
minutes  by  multiplying  by  6 ;  name  the  true  amplitude  East  if  a.m. 
at  ship,  but  West  if  p.m.,  and  towards  the  North  or  South  according 
as  the  declination  is  North  or  South. 

The  remainder  of  the  problem  may  be  worked  the  same  as  in 
the  longer  method,  but  we  advise  the  following  rule  for  practice,  as 
it  entirely  does  away  with  the  misleading  term,  error  of  compass . 

Rule  for  Practice  at  Sea. — Take  from  the  chart  the  variation  and 
apply  it  to  the  true  amplitude,  allowing  East  to  the  left  and  West 
to  the  right.  The  result  will  be  the  magnetic  amplitude,  or  what 
the  compass  would  indicate  provided  there  were  no  deviation  on  it. 

To  the  magnetic  amplitude  apply  the  bearing  by  compass.  The 
difference  will  be  the  deviation,  which  must  be  named  East  if  the 
magnetic  hearing  is  to  the  right  of  the  compass,  and  West  if  to  the 
left. 

Sa7ne  Two  Examples  Worked  with  Table    39    of    the     Bowditch 
'     Epitome. 


Lat.  nearest  degree  50°  N. 
Decl.  21°  S. 

T.  amp. 
Var. 


33^ 


E.  33    54  S. 
22    10  E. 


Mag.  amp.     E.  11    44  S. 
Comp.  amp.  E.  11    15  S. 

Dev.  00°29'E. 


Lat.  nearest  degree  31°  N. 
Decl.  15°  N. 


17' 


W.  17    36  N. 
27    51  E. 


T.  amp. 
Var. 

Mag.  amp.    W.  10    15  S. 
Comp.  amp.  W.    2    49  8. 

Dev.  T°  26'  W. 


Deviation.  17? 


The  very  flight  discrepancy  existing  between  the  two  methods  has 
no  practical  significance,  as  the  observer  is  likely  to  make  an  error 
in  the  observed  bearing  larger  than  the  difference  between  the  two 
methods,  and  it  is  also  almost  impossible  to  steer  a  course  inside  of 
a  degree,  even  on  board  the  finest  steamer  with  its  modern  steering- 
gear  and  excellent  conipasses. 

SHORT   METHOD   OF   WORKING   AMPLITUDE   BY   THE 
AMERICAN  AZIMUTH  TABLES. 

Enter  the  table  with  the  nearest  degree  of  latitude  and  declina- 
tion, being  careful  to  note  if  they  are  of  the  same  name  or  of  con- 
trary names ;  look  at  the  bottom  of  the  page,  under  the  nearest  de- 
gree  of  declination,  and  the  time  of  the  object's  rising  or  setting, 
with  its  true  bearing  at  the  time,  will  be  found;  mark  down  this 
true  bearing  and  name  it  according  to  the  rules  printed  at  the  bot- 
tom of  the  page,  which  are: 

In  South  latitude,  and  time  a.m.,  read  the  bearing  from  S.  to  E. 
In  South  latitude,  and  time  p.m.,  read  the  bearing  from  S.  to  W. 
In  North  latitude,  and  time  a.m.,  read  the  bearing  from  N.  to  E. 
In  North  latitude,  and  time  p.m.,  read  the  bearing  from  N.  to  W. 

When  the  true  bearing  or  azimuth  has  been  properly  named,  apply 
the  variation,  allowing  East  to  the  left  and  West  to  the  right.  The 
result  will  be  the  magnetic  hearing.  Then  take  the  difference  be- 
tween the  magnetic  and  compass  bearings,  and  the  result  will  be 
the  deviation,  to  be  named  East  if  the  magnetic  hearing  is  to  the 
right  of  the  compass-bearing,  but  West  if  to  the  left. 

Same  Two  Amplitudes  Worked  with  the  American  Azimuth  Tables. 

Lat.    50°  N.  j  ^.    1230  53,  E.     t,  ^,_ 
Decl.21°S.   i        180    qq 

S.     56    07   E.     T.  az. 
22    10   E.     var. 

S.     78    17   E.     mag.  az. 
S.     78    45   E.     comp.  az. 

00°  28'  E.     dev. 

Taylor's   Mod.  Nav.   12. 


178  Taylor's  Moderx  Xavigation. 


Lat.    31°  N.  )  j^     ^2°  26'  W.     T. 


Decl.  15°  N  J     '27    51   e 


az. 


var. 


N.  100    17   W.     mag.  az. 
180    00 


S.     79    43  W.     mag.  az. 
S.     87    11   W.     comp.  az. 

r  28'  W.     dev. 

The  three  methods,  it  will  be  noticed,  practically  coincide ;  there- 
fore the  navigator  may  use  either  one  of  them  with  the  greatest 
confidence  when  at  sea. 

Examples  for  Prarticc. — May  he  Worl-ed  by  Either  of  the  Three 
Methods  Given. 

1894,  March  4th,  at  e""  20^^  a.m.,  A.T.S.  in  lat.  39°  51'  N.  and 
long.  132°  50'  W.;  sun's  obs.  amp.  E.14S.;  var.  18°  10'  E.  Re- 
quired the  deviation  for  the  direction  of  ship's  head  at  time  of  ob- 
servation. 

Anstcer.—G.A.T.  March  4*^  3^^  11°^  20^;  cor.  decl.  6°  16'  25"S.; 
T.  amp.  E.  8°  10'  S. ;   error  5°  21'  E. ;   dev.  12°  49'  W. 

1894,  December  2d,  at  8''  50°^  p.m.,  A.T.S.,  in  lat  59°  40'  S.  and 
long.  168°  E.;  sun's  obs.  amp.  S.  2°  E. ;  var.  23°  00'  E.  Required 
the  deviation  for  the  direction  of  ship's  head  at  time  of  observation. 

Answer.— G.A.T.  December  1''  21'^  38"^  00^  cor.  decl.  22°  00'  6" 
S.;  T.  amp.  W.  47°  53'  S.;  error  44°  7'  E. ;  dev.  21°  7'  E. 

1894,  August  1st,  at  10"  20'"  p.  m.,  A.T.S.,  in  lat.  69°  59'  N.  and 
long  18°  3'  E.;  sun's  obs.  amp.  N.XW.;  var.  16°  17'  W.  Required 
the  deviation  for  the  direction  of  ship's  head  at  time  of  observation. 

Answer.— G.A.T.  August  1^  9"  7°^  48^;  cor.  decl.  17°  52'  37"  N.; 
T.  amp.  W.  63°  47'  N.;  error  14°  58'  W.;  dev.  1°  19'  E. 

1894,  December  1st,  at  9"  0"  p.  m.,  A.T.S.,  in  lat.  60°  S.  and  long. 
16°  E.;  sun's  obs.  amp.  S.W'.14W. ;  var.  23°  10'  E.  Required  the 
deviation  for  direction  of  ship's  head  at  time  of  observation. 

Answer.— Cor.  decl.  21°  51'  11"  S. ;  T.  amp.  W.  48°  6'  S.;  error 
5°  55'  W.;  dev.  29°  05'  W. 

1894,  June  3d,  at  3"  38""  p.m.,  A.T.S.,  in  lat.  52°  30'  N.  and 


Deviation.  179 


long.  92°  10'  W.;  sun's  obs.  amp.  N.W.XW.;  var.  26°  00'  E.  Re- 
quired the  deviation  for  direetion  of  sliip's  head  at  time  of  observa- 
tion. 

Answer.— Cot.  decl.  22°  24'  13"  N.;  T.  amp.  W.  38°  45'  N. ; 
error  5°  0'  E.;  dev.  21°  0'  W. 

1894,  November  1st,  at  6^  30'"  a.m.,  A.T.S.  in  lat.  18°  59'  N.  and 
long.  157°  10'  W. ;  sun's  obs.  amp.  E.XS.i/aS. ;  var.  10°  20'  W.  Re- 
quired the  deviation  for  direction  of  ship's  head  at  time  of  observa- 
tion. 

Ansiver.—Cov.  decl.  14°  35'  38"  S.;  T.  amp.  E.  15°  28'  S. ;  error 
1°  2o'  W.;  dev.  8°  55'  E. 

1894,  March  20th,  at  6^  lO'"  p.m.,  A.T.S.,  in  lat.  54°  58'  X.  and 
long.  148°  W.;  sun's  obs.  amp.  W.  2°  S.;  var.  17°  10'  E.  Required 
the  deviation  for  direction  of  ship's  head  at  time  of  observation. 

Answer.— Cot.  decl.  0°  12'  58"  N.;  T.  amp.  W.  0°  23'  N.;  dev. 
U  °  47'  W. 

1894,  September  2d,  at  6^  40°^  p.m.,  A.T.S.,  in  lat.  44°  29'  N. 
and  long.  36°  12'  E. ;  sun's  obs.  amp.  W.X^.;  var.  5°  40'  0"  W. 
Required  the  deviation  for  direction  of  ship's  head  at  time  of  ob- 
servation. 

Answer.— Dew.  5°  20'  E. 

1894,  October  26th,  at  7'>  14"^  a.m.  A.T.S.,  in  lat.  53°  5'  X.  and 
long.  90°  40'  E.;  sun's  obs.  amp.  E.S.E.;  var.  7°  40'  E.  Required 
the  deviation  for  direction  of  ship's  head  at  time  of  observation. 

Answer.— Dew  9°  15'  W. 

1894,  'July  31st,  at  6^^  40°^  p.m.,  A.T.S.,  in  lat.  26°  55'  X.  and 
long.  179°  29'  E.;  sun's  obs.  amp.  X.  89°  W.;  var.  12°  57'  E.  Re- 
quired the  deviation  for  the  direction  of  ship's  head  at  time  of 
observation. 

Answer.— T)c\.  6°  39'  E. 

1894,  May  1st,  at  5'*  2°^  a.m.,  A.T.S.,  in  lat.  47°  8'  N. ;  long.  160° 
40'  E.;  sun's  obs.  amp.  N.E.X^^.;  var.  5°  30'  E.  Required  the  de- 
vit^tion  for  direction  of  ship's  head  at  time  of  observation. 

Answer.— Dew  28°  29'  E. 

1894,  October  31st,  at  7^  20"^  a.m.,  A.T.S.,  in  lat.  53°  50'  N.  and 
long.  170°  E.;  sun's  obs.  amp.  was  E.  11°  15'  S.;  var.  30°  40'  E. 
Required  the  deviation  for  direetion  of  ship's  head  at  time  of 
observation. 

A7iswer.—J)e\.  17°  45'  ^Y. 


180  Taylor's  Modern  Xavigation. 

1894,  June  26th,  at  6^  10""  p.  m.,  A.T.S.,  in  lat.  0°  10'  S.  and 
long.  15°  10'  W.;  sun's  obs.  amp.  W.S.W.i^S.;  var.  22°  10'  E. 
Required  the  deviation  for  direction  of  ship's  head  at  time  of 
observation. 

Answer.— Bev.  26°  30'  E. 

1894,  May  17th,  at  4:^  40'"  a.  m.,  A.T.S.,  in  lat.  45°  52'  X.  and 
long.  136°  51'  E.;  sun's  obs.  amp.  E.X.E. ;  var.  5°  40'  W.  Ee- 
quired  the  deviation  for  direction  of  ship's  head  at  time  of  obser- 
vation. 

Answer. — Dev.  0°  4'  W. 

THE  ALTITUDE  AZIMUTH. 

The  azimuth  and  amplitude  problems  are  both  used  to  ascertain 
the  deviation,  but  the  observations  differ  in  one  respect;  viz.,  the 
amplitude  is  observed  when  the  object  is  rising  or  setting,  whereas 
the  azimuth  is  taken  at  any  time  when  the  sun  is  above  the  horizon, 
provided  its  altitude  is  not  greater  than  60°. 

The  Observation. — Take  a  bearing  by  the  ship's  compass,  meas- 
ure the  altitude  with  the  sextant  and  note  the  mean  time  at  ship 
or  the  chronometer  time,  being  careful  to  note  also  the  course  the 
ship  was  on  at  the  time,  as  the  deviation  found  will  be  for  that 
course  only. 

Rule. 

First  Case. — If  mean  time  at  ship  was  taken. 

If  it  is  A.M.  at  ship,  add  12  to  the  hours  and  put  the  date  one  day 
back. 

If  it  is   P.M.  at  ship,  mark  down  the  date  and  time  as  they  stand. 

The  result  in  both  cases  will  be  the  astronomical  mean  time  at 
ship,  to  which  must  be  applied  the  longitude  in  time,  adding  if 
West,  subtracting  if  East.  The  result  will  then  be  the  astronomical 
mean  time  at  Greenwich. 

Second  Case. — If  time  by  chronometer  is  noted,  apply  its  error, 
if  any.    The  result  will  be  G.M.T. 

Take  out  of  the  Nautical  Almanac  the  sun's  declination  and  cor- 
rect it  for  the  G.M.T.  and  find  the  P.D.;  correct  the  altitude  as 
usual;  mark  down  the  P.D.,  latitude,  and  true  altitude  under  one 
another,  add  them,  and  divide  the  sum  by  2;  this  is  the  half-sum; 
subtract  the  half-sum  from  the  P.D.  or  P.D.  from  half  sum  as  the 
case  iiiav  be  and  call  wliat  is  left  the  remainder. 


Deviation.  181 


Take  out  of  Table  44  the  secant  of  the  hititude,  secant  of  the 
true  altitude,  cosine  half-sum,  cosine  remainder  (throwing  away 
the  lO's  from  the  index)  ;  add  these  logs,  and  divide  the  sum  by  2 ; 
the  remainder  will  be  the  sine  of  half  the  azimuth;  look  for  this 
half-sum  of  logs,  in  the  sine  column,  and  when  found  note  the  de- 
grees at  the  top  and  minutes  to  the  left  if  you  read  sine  from  the 
top,  but  if  you  read  sine  from  the  bottom  read  degrees  at  the  bot- 
tom and  minutes  to  the  right ;  multiply  these  degrees  and  minutes 
by  2 ;  the  result  will  be  the  true  azimuth. 

To  Name  the  True  Azimuth. — Xame  the  true  azimuth  opposite 
to  the  latitude,  and  towards  the  East  if  a.m.,  and  towards  the  West 
if  P.M. 

Under  the  true  azimuth  put  the  observed  azimuth,  adding  if  they 
are  of  different  names  and  subtracting  if  same  names;  the  result 
will  be  the  error. 

To  Name  the  Error. — Stand  in  the  center  of  the  compass  and 
look  towards  the.  true  azimuth ;  then  if  the  true  azimuth  is  to  the 
right  of  the  observed  azimuth,  the  error  is  East ;  if  to  the  left,  the 
error  is  West. 

Under  the  error  put  the  variation;  add  them  if  different  names 
and  subtract  them  if  the  same  name;  the  result  will  be  the  devia- 
tion. 

To  Name  the  Deviation. — Stand  in  the  center  of  the  compass 
and  look  at  the  North  point;  then  if  the  error  is  to  the  right  of 
the  variation,  the  deviation  will  be  East;  if  to  the  left,  the  devia- 
tion will  be  West. 

Note. — By  the  rules  given  in  Bowditch  the  half-sum  of  logs  i? 
called  cosine,  and  in  this  ease  the  true  azimuth  must  be  named 
the  same  as  the  latitude. 

Example.— 18di,  March  3d,  at  4"  36"^  10«  p.m.,  M.T.S.,  in  lat. 
31°  14'  IST.  and  long.  174°  00'  W.;  sun's  bearing  by  compass  (obs. 
az.)  S.  80°  W.;  obs.  alt.  of  sun's  L.L.  16°  49'  00" ;  eye  16  feet;  var. 
14°  20'  E. ;  ship's  head  N.E.  Required  the  deviation  of  the  com- 
pass for  the  position  of  the  ship's  head  at  time  of  taking  the  ob- 
servation. 

March    3''  04*^  36"^  10"  M.T.S.  Long.  174°  00'  W. 

+  11    36     00  4 


3    16    12     10  M.T.G.  60)69  6     00 

24    00     00  11^  36-  00" 

-j-h  4j^m  from  nearest  noon. 


IS-:- 


Taylor's  Modern  Xavigatiox. 


Decl.           6°  19'  41"  S. 

Diff.  1  hour. 

7  31 

57".81 

Cor.  decl.    6    27   12    S. 

7  .8 

90    00  00 

46248 

P.D.          96°  27'  12" 

40467 

60)450.918 

"31' 


Obs.  alt.  16°  49'  00" 
+  9  13 


T.  alt.      16°  58'  13" 


Parlx.    0'  08" 
S.D.     16  10 

+  16  18 

-  7  05 

+  9^3' 


Dip  3'  55' 
Ref.  3   10 

-7^' 


P.D.  96°  27'  12" 

Lat.  31    14  00    sec     .06800 

T.  alt.        16    58  13    sec     .01933 


2)144    39  25 

Half-sum  72    19  42    cos  9.48213 
P.D.  96    27   12 


Rem.         24°  07'  30"  cos  9.96034 

2)19.52980 

sine  9.76490 


35°  35' 
2 

T.  az.      S.  71    10  W. 
Obs.  az.  S.  80    00  W. 

Error  8    50   W. 

Var.  14    20  E. 


Dev. 


23°  10'  W. 


\v- 


E     N     V 


The  deviation  for  ship's  head  N.E.  is  therefore  23°  10'  W. 

Example.— lSd4:,  February  5th.  8^  18*"  58*  a.m.,  M.T.S.,  in  lat. 
14°  32'  N.  and  long.  148°  E. ;  sun's  bearing  by  compass (obs.az.) 


Deviation. 


183 


S.  80°  42'  E.;  obs.  alt  L.L.  25°  59'  00";  eye  30  feet;  var.  6°  10' 
E. ;  ship's  head  N.N.W.  Eequired  the  deviation  of  the  compass 
for  the  position  of  the  ship's  head  at  the  time  of  observation. 


Feb. 


5<'    8"  18"^  58-^  A.M. 
12 


M.T.S.  4   20    18    58 

9    52     00   E. 


M.T.G.  4"  10^^  26'"  58« 


Long.  148°  E. 
4 


60)592 


52™  00« 


2)146    40  30 


Half-sum    73    20  15     cos  9.45758 
P.D.  106    00  28 


Rem. 


32°  40'  13"  cos  9.92522 
2)19.44375 


Decl.          16° 

08'  17" 
7  49 

S. 
S. 

106 
14 

26 

ir.  in  1  hour. 
45"  .12 
10    .4 

Obs.  alt 
Dip, 

Refr. 

S.D. 
Parlx. 

T.  alt. 

.01412 

.04683 

25°  59'  00" 
-  5  22 

Cor.  decl.  16 

00  28 
00  00 

00'  28" 

P.D. 
Lat. 
T.  alt 

25    53  38 

90 

18048 
45120 

-   1  59 

P.D.         106° 

25    51   39 

60)469.248 

7'  49" 

=>  00'  28" 
32  00     sec 
08  02     sec 

+  16   15 

+         8 

26°  08'  02" 

sine  9.72187 


31° 

48' 

S 

2 

T.  az. 

63 

36 

E. 

Obs.az 

.S 

80 

42 

E. 

Error         17    06  E. 
Var.  6    10  E. 


Dev. 


10°  56'  E. 


The  deviation  for  ship's  head  N.N.W.  is  therefore  10°  56'  E. 


ISi  Taylor's  Modern  Xavigatiox. 

Example. — ^^January  Tth,  p.m.,  at  ship,  in  lat.  5°  21'  N".  and  long. 
163°  E.;  sun's  bearing  by  compass  (obs.  az.)  S.  87°  W.;  time  by 
chronometer  G**  17'^  48°^  39%  which  was  30^  fast  of  G.M.T.;  obs. 
alt.  of  sun's  L.L.  17°  20'  00";  I.E.— 20";  eye  16  feet;  var.  25°  40' 
W.  Eequired  the  deviation  of  the  compass  lor  the  position  of 
the  ship's  head  at  the  time  of  observation. 


Jan.  6-^  17*^  48'"  39«  Decl.      22°  20'  37"  S.       Diff.  1  hour 

30  2   01"  19".5 

6.2 


gd  i7h  4gm    gs  G.M.T    Cor.  D.  22°  22'  38"  S. 

90    00  00  39  0 

1170 

60)120.90 


P.  D.    112°  22'  38" 


Obs.  alt.  17°  20'  00" 
I.  E.  20 


Dip 


Refr. 


S.  D. 
Par. 


17 

19 

40 

3 

55 

17 

15 

45 

3 

5 

17 

12 

40 

4- 

16 

18 

+ 

8 

T.  Alt.       17°  29'    6" 


P.  D.  112°  22' 38" 

Lat.  5    21   00       sec     .00190 

T.  alt.  17    29  06       sec     .02054 


2)135    12  44 

Half-sum  67  36~22   cos  9.58101 
P.  D.    112  22  38 

Rem.     44°  46'  16"  cos  9.85125 

2)1^45470 

Sine  9.72735 


2'1' 


Deviation. 


32^ 


16' 
2 


T.  az.     S.  64     32   W. 
Obs.az.  S.  87    00    W.  W 


Error  22    28    W.    0 

Var.  25    40    W . 


Dev. 


3°  12'   E. 


iS 


185 


Examples  for  Practice. 

1894,  June  13th,  a.m.,  at  ship,  in  lat.  34°  20'  S.  and  long.  49°  00' 
E.;  sun's  obs.  az.  E.XS.i^S.;  sun's  obs.  alt.  L.L.  12°  50'  00"; 
chron.  showed  June  12^  17^  12'°  4%  which  was  fast  of  G.M.T.  3°^ 
12«;  eye  18  ft.;  I.E.+l'  10";  var.  22°  50'  W.  Find  the  deviation 
of  the  compass  for  direction  of  ship's  head  at  time  of  observation. 

Answer.— GM.T.  12"'  1?''  8""  52«;  cor.  decl.  23°  13'  19"  N".;  T. 
alt.  12°  58'  46";  half-sum  of  logs.  9.62314;  T.  az.  N.  49°  40'  E. ; 
error  54°  24'  W.;  deviation  31°  34'  W. 

1894,  June  14th,  7''  12™  50«  p.m.,  M.T.S.,  in  lat.  54°  50'  N.  and 
long.  69°  50'  W.;  sun's  obs.  az.  N.N.W.;  obs.  alt.  L.L.  9°  10'  10"; 
I.E.— 1'  10";  eye  18  ft.;  var.  50°  40'  W.  Find  deviation  of  com- 
pass for  direction  of  ship's  head  at  time  of  observation. 

Ariswer.— G.M.T.  W^  IP  52'"  10^;  cor.  decl.  23°  18'  45"  N.;  T. 
alt.  9°  15'  0";  half-sum  of  logs.  9.93242;  T.  az.  S.  117°  43'  W.; 
dev.  10°  52'  E. 

1894,  November  1st,  a.m.  at  ship,  in  lat.  49°  52'  X.  and  long. 
28°  3'  W.;  sun's  obs.  az.  S.XE.;  alt.  of  sun's  L.L.  12°  2';  I.E. 
—2'  15" ;  eye  18  ft. ;  time  by  chron.  October  31'»  22''  16°"  58%  which 
was  1°^  18«  slow  of  G.M.T.  var.  22°  20'  W.  Find  the  deviation  for 
direction  of  ship's  head  at  time  of  observation. 

Answer.— G.M.T.  October  31'^  22''  18°'  16«;  cor.  decl.  14°  30' 
30"  S.;  T.  alt.  12°  7'  28";  half-sum  of  logs.  9.62003;  T.  az.  S.  49° 
16'  E.;  dev.  15°  41'  W. 

1894,  September  26th,  8"  40'°  a.^^l,  M.T.S..  in  lat.  13°  58'  N. 
and  long.  174°  53'  W. ;  sun's  obs.  az.  E.^S. ;  obs.  alt.  sun's  L.L. 
38°  45'  15";  I.E.  +2'  10";  eye  20  ft.;  var.  13°  10'  E.  Find  de- 
viation for  direction  of  ship's  head  at  time  of  observation. 


186  Taylor's  Modern  Xavigation. 


Answer.— Cov.  decl.  1°  28'  28"  S.;  T.  alt.  38°  58'  00";  half-sum 
of  logs.  9.79129;  T.  az.  S.  76°  24'  E. ;  error  5°  10'  E. ;  dev.  8° 
00'  W. 

1894,  April  2d,  p.  m.  at  ship,  in  lat.  50°  3'  N.  and  long.  153°  10' 
E.;  sun's  obs.  az.  W.  2°  S.;  obs.  alt.  sun's  L.L.  12°  1'  40";  eye  20 
ft. ;  time  by  chron.  April  1^  18*^  56""  49^  which  was  2-"  10«  slow  of 
G.M.T.;  var.  10°  10'  E.  Find  deviation  for  direction  of  ship's 
head  at  time  of  observation. 

A7iswer.—CoT.  decl.  4°  57'  5"  N. ;  T.  alt.  12°  9'  1" ;  half-sum  of 
logs.  9:82194;  T.  az.  S.  83°  10'  W.;  dev.  15°  00'  W. 

1894,  June  15th,  a.^i.  at  ship,  in  lat.  33°  49'  S.  and  long.  50°  10' 
E.;  sun's  obs.  az.  E.XS.;  obs.  alt.  of  sun's  L.L.  12°  46'  10";  LE. 
—2'  40" ;  eye  27  ft. ;  time  by  chron.  June  U^  16'^  59°^  50«  G.M.T. ; 
var.  1°  30'  E.  Find  deviation  for  direction  of  ship's  head  at  time 
of  observation. 

Answer.— Cot.  decl.  23°  19'  16"  N. ;  T.  alt.  12°  50'  08"  ;  half-sum 
of  logs.  9.62690;  T.  az.  X.  50°  8'  E.;  dev.  52°  37'  W. 

TIME  AZIMUTHS. 

A  Bide  to  Find  the  Deviation  of  the  Compass,  Using  the  American 
Azimuth  Tables. 

The  altitude  azimuth  problem  is  used  mostly  when  passing  ma- 
rine board  examinations,  or  when  the  azimuth  tables  are  not  to 
be  obtained,  but  the  tables  are  so  cheap,  that  you  will  rarely  find  a 
vessel  without  one  or  more  copies  on  board.  They  are  useful  not 
only  in  finding  the  deviation,  but  also  in  working  observations,  as 
explained  in  another  part  of  this  work. 

There  are  several  good  azimuth  tables  in  use,  but  as  this  is  an 
American  work  we  will  explain  only  the  one  published  by  the 
Hydrographic  Oflfico. 

Explanation  of  How  to  Open  the  Book.—li  the  latitude  and  dec- 
lination have  same  name,  open  the  first  part  of  book,  but  if  differ- 
ent names,  the  last  part. 

At  the  top  of  the  page  is  given  the  declination,  from  0°  to  23°. 

On  the  loft-hand  side,  the  apparent  time.  a.m. 

On  the  right-hand  side,  the  apparent  time.  p.m. 

At  till'  bottom  is  given  the  time  of  sun">  rising  and  sun's  setting, 
with  thr  sun's  true  azimuth  at  those  time-,  and   under  these  are 


Deviatiox.  18' 


printed  the  rules  to  name  the  azimuth,  making  it  unnecessary  for 
the  navigator  to  memorize  a  rule. 

It  will  be  noticed  that  the  time  at  the  sides  is  given  for  every 
ten  minntes,  therefore  the  sun's  true  azimuth  may  be  found  by 
simple  inspection  for  every  ten  minutes  of  time.  We  think,  how- 
ever, that  the  tables  would  be  of  much  more  value  to  the  navigator 
if  the  azimuths  were  given  for  every  five  minutes,  for,  as  they 
are  at  present  arranged,  it  is  necessary  to  interpolate  if  the  A.T.S. 
is  not  on  the  even  ten  minutes. 

The  first  and  most  important  element  required  when  using  these 
tables  is  the  A.T.S.,  a  knowledge  of  which  must  be  within  one  min- 
ute of  the  actual  time. 

The  other  elements  are,  the  latitude  to  the  nearest  degree  and  the 
declination  to  the  nearest  degree,  but  if  greater  accuracy  is  re- 
quired, work  to  half-degrees  and  interpolate.  As  most  seamen  have 
very  little  knowledge  in  regard  to  ascertaining  the  correct  A.T.S., 
for  use  in  this  question  we  will  here  give  several  rules  to  obtain  the 
same,  meeting,  we  think,  any  case  that  is  likely  to  occur  on  either 
an  ocean  liner  or  a  coasting-schooner. 

First  Method. — To  Set  a  Watch  or  Wheelhoii.se  Clock  to  Apparent 
Time  Sufficiently  Near  to  Work  the  Time  Azimuth. 

Take  a  watch  and  compare  it  with  a  chronometer,  marking  both 
times  down ;  to  the  time  shown  on  the  chronometer  apply  its  error ; 
this  will  give  the  G.M.T. ;  take  from  the  Nautical  Almanac,  page  2 
of  the  month,  the  equation  of  time  and  apply  it  to  the  G.M.T.  as 
stated  at  the  top  of  the  column  ;  this  will  give  the  G.  A.T. ;  next  take 
the  longitude  of  the  ship,  convert  it  into  time,  and  apply  it  to  the 
G.A.T.  by  adding  when  in  East  longitude,  and  by  subtracting  when 
in  West  longitude.  This  will  give  the  ship's  apparent  time  at  the 
instant  of  comparing  the  watch  with  the  chronometer;  note  the 
difference  between  this  correct  ship's  apparent  time  and  what  the 
watch  showed,  and  then  put  the  watch  ahead  or  back,  according  to 
the  difference  found;  you  will  now  have  ship's  apparent  time  on 
the  watch,  and  will  be  ready  to  takv  any  number  of  time  azimuths, 
provided  tlie  ship  does  not  change  her  longitude  more  than  15'. 

E.vamples  in  Correcting  a  Watch. 

1894,  January  ITth.  a.m.  at  ship,  in  long.  120°  W. ;  time  by 
watch  3^  10™,  and  at  same  instant  a  chronometer  showed 
ll'^  lO'"  15«  G.M.T.     Find  error  of  watch  on  A.T.S. 


188  Taylor's  Modern  Xavigation. 


Chron.       11'^  10'"  15«  G.M.T.  Long.  120°  \V. 

Equa.    -         10     24  4 

io~59     51    G.A.T.  60)480 

-_^^0_00  W.  ^,— 


2  59     51    S.A.T. 

3  10     00   watch  time 


Chron.         P 
Equa.     — 

50'" 
13 

51«  G.M.T. 

57 

1 
+  11 

1 
1 

36 
31 

~08~ 
20 

54   G.A.T. 
20   E. 

"U   S.A.T. 
00  watch  time 

Watch  is 

IP^ 

46«  fast  of  A.T.! 

Watch  is         10-"    9«  fast  of  A.T.S. 

1894,  February  2d,  p.m.  at  ship,  in  long.  172°  50'  E. ;  time  by 
watch  I''  20™,  and  at  same  instant  a  chronometer  showed 
1"^  50"°  51«  G.M.T.  Find  the  error  of  watch  on  A.T.S. 

Long.         172°  50'  E. 
4 

60)691    20 

11*^  31'"  20^ 


Examples  for  Practice. 

March  18th,  a.m.  at  ship;  time  by  watch  7^  12"^,  and  at  same 
instant  a  chronometer  showed  O''  40'"  10«  G.M.T.;  long.  75°  27'  W. 
Find  error  of  watch  on  A.T.S. 

Answer. — 18""  14®  slow. 

May  27th,  p.m.  at  ship;  time  by  watch  9''  46"",  and  at  same  in- 
stant a  chronometer  showed  ll*^  53'"  10®  G.M.T.;  long.  147°  25'  E. 
Find  error  of  watch  on  A.T.S. 

Answer. — O**  0™  5®  fast. 

June  30th,  a.m.  at  ship;  time  by  watch  9*^  40'";  a  chronometer 
showed  8"^  46™  G.M.T.;  long.  17°  15'  E.  Find  error  of  watch  on 
A.T.S. 

Answer. — ll""-  3G®  slow. 

July  20th,  a.m.  at  ship;  time  by  watcl\  2"  12'";  a  chronometer 
showed  7^  47""  17®  G.M.T.;  long.  79°  41'  W.  Find  error  of  watch 
on  A.T.S. 

Aiisircr. — 10'"  2r)''  sh)w. 


Deviation.  189 


Second  Method. — To   Find  the  Apparent   Time    at    Ship    When 
There  is  no  Chronometer  on  Board. 

First  Case. — It  is  presumed  that  the  navigator  is  in  possession 
of  a  good  watch  that  will  not  alter  more  than  one  minute  in  a 
week.  Set  this  watch,  before  leaving  port,  to  Pacific  Standard 
Time,  which  is  calculated  for  120°  West  longitude,  and  is  therefore 
8  hours  slow  of  Greenwich  M.T. ;  for  every  degree  that  you  are  to 
the  West  of  120°  put  the  watch  back  4  minutes  of  time,  and  for 
every  degree  that  you  are  to  the  East  of  120°  put  the  watch  ahead 
4  minutes  of  time;  this  will  give  the  M.T.S.;  take  from  the  Nauti- 
cal Almanac,  on  page  2  of  the  month,  the  equation  of  time  and  ap- 
ply it  to  the  M.T.S.  as  stated  on  the  top  of  the  column ;  this  will 
give  the  A.T.S.  sufficiently  near  to  work  the  time  azimuth. 

Second  Case. — If  the  vessel  is  on  the  Atlantic  coast,  where  the 
time  is  calculated  for  75°  West  longitude,  then  you  would  be  5 
hours  slow  of  G.M.T. ;  then  for  every  degree  that  you  are  to  the 
West  of  75°  put  the  watch  back  4  minutes  of  time,  and  for  every 
degree  that  you  are  to  the  East  of  75°  put  the  watch  ahead  4  min- 
utes of  time;  this  will  give  the  M.T.S. ;  take  from  the  Nautical  Al- 
manac, on  page  2  of  the  month,  the  equation  of  time  and  apply  it 
to  the  M.T.S.  as  stated  at  the  top  of  the  column;  this  will  give  the 
A.T.S.  sufficiently  near  to  work  the  time  azimuth. 

The  preceding  method.&'  of  determining  the  A.T.S.  being  thor- 
oughly understood,  and  the  navigator  having  set  his  watch,  we  will 
now  proceed  to  give  the  time  azimuth  worked  out  in  full. 

The  Observation. — Take  a  bearing  of  the  sun  by  the  ship's  com- 
pass or  Pelorus — this  will  be  the  compass-bearing,  or  observed  azi- 
muth— and  at  the  same  instant  note  the  time  by  a  watch  which 
has  been  previously  set  to  A.T.S,,  and  also  note  the  direction  of  the 
ship's  head  at  time  of  taking  the  bearing;  turn  up  the  azimuth 
tables  being  very  careful  in  regard  to  the  latitude  and  declination 
having  same  name  or  contrary  names,  and  find  the  required  degree 
of  latitude;  when  found,  look  at  top  of  page  for  the  declination, 
and  under  it,  abreast  of  the  A.T.S.,  will  be  found  the  sun's  true 
azimuth,  which  must  be  named  according  to  the  rule  printed  at  the 
bottom  of  each  page;  then  if  the  degrees  are  more  than  90,  sub- 
tract them  from  180°  and  change  the  North  to  South,  or  the  South 
to  North,  but  keep  the  name  of  East  or  West;  under  the  true  azi- 
muth place  the  variation,  allowing  East  to  the  loft  and  West  to  the 


190  Taylor's  Moderx  Navigatiox. 

right;  the  result  will  be  the  magnetic  azimuth;  under  the  magnetic 
azimuth  mark  the  observed  azimuth,  and  find  the  difference  by 
adding  them  when  contrary  names  and  subtracting  when  same 
name;  the  result  will  be  the  deviation,  to  be  named  East  if  the 
magnetic  bearing  is  to  the  right  of  the  compass-bearing,  but  West 
if  to  the  left. 

The  following  examples  illustrate  the  practical  application  of 
this  method,  and  the  navigator  is  advised  to  study  them  thoroughly, 
as  they  are  very  important  in  modern  navigation. 

Example  in  Finding  the  Error  of  a  Watch  and  the  Deviation  by  a 
Time  Azimuth. 

1894,  February  12th,  a.m.  at  ship,  in  lat.  43°  S.  and  long.  74° 
18'  W. ;  time  by  watch  6^  54™,  and  at  same  instant  a  chronometer 
showed  11^"  59™  3P  G.M.T.;  the  supposed  obs.  az.  S.  82°  E.;  var. 
22°  14'  W.  Eind  the  deviation  for  the  direction  of  the  ship's  head 
at  time  of  observation. 


Chron.  11'^  59'"  3P  G.M.T.  Long.  74°  18'  W. 

4 


11*^ 

59™ 
14 

3P 
26 

G.M.T. 

11 

4 

45 

57 

05 
12 

G.A.T. 
W. 

6 
6 

47 

54 

53 
00 

A.T.S. 

60)297    12 


Watch  time 

Watch  6"^  07^  fast  of  A.  T.  S. 


A.T.S.  6^'  48'"  A.M.  ) 

Lat.      42°  S.  [  T.  az.  S.  87°  42'  E. 

Decl.  13^°  S.  )         Var.  22    14  W.  allowed  right. 

S.  65    28   E.  mag.  az. 
S.  82    00  E.  comp.  az. 

Dev.  16°  32'  E. 

It  will  be  noticed,  when  entering  the  tables,  that  the  A.T.S.  does 
not  fall  exactly  on  the  ten  minutes;  therefore  we  must  interpolate 
after  the  following  manner :  Take  the  two  azimuths  on  each  side 
of  the  time  and  find  the  change  of  bearing  in  ten  minutes  by  sub- 
tracting the  lesser  from  the  greater ;  divide  this  change  by  10  and 
we  have  the  change  in  one  minute,  which  must  be  multiplied  by 


Deviation.  191 


the  odd  number  of  niinutes  in  the  A.T.S.  \\1ien  a  half-degree  of 
declination  is  used,  take  the  mean  of  the  two  azimuths  on  either  side 
of  the  declination  given. 

The  student  is  recommended  to  work  the  examples  given  of  the 
altitude  azimuth  jjroblems  by  the  Time  Azimuth  Tables,  which 
may  be  done  by  simply  finding  the  A.T.S.  from  the  time  given, 
ignoring  entirely  the  altitude  and  its  correction. 

Example. — August  18th.  p.m.  at  ship;  time  by  chron.  0**  51"°  18' 
G.M.T.;  obs.  az.  S.  77°  30'  W. ;  var.  10°  15'  W.;  lat.  40°  N. ;  long. 
124°  50'  W.    Find  the  deviation  by  time  azimuth. 


Chron.     0'>  51'"  18^^  G.M.T.  Lonij.      124"50'  W. 

-        3     40  4 


0    47     38    G.A.T.  60)499    20 

-8_^J0    W.  ----2„, 


4h  28"!  18"  A.T.S. 


A.T.S.  41^  28'"  P.M.   ) 

Lat.  40°  N.        \  T.  az.  N.         94°  37'  W. 

Decl.         13    N.        )  Var.  10    15    W. 

Mag.  az.  N.    84    22    W. 
Comp.  az.  S.  77    30    W. 


161    52 
180    00 

Dev.  18°  8'  E. 


TIME  AZIMUTHS  BY  STARS  OR  PLANETS. 

The  most  important  part  of  this  problem  is  the  finding  of  the 
star's  hour-angle. 

Rule. 

Take  a  bearing  of  the  star  by  ship's  compass  and  note  the  time 
by  a  chronometer.     Apply  the  error,  if  any,  and  get  the  G.M.T. 


192  Taylor's  ]\Iodekn  Navigation. 


To  the  G.M.T.  apply  the  longitude  in  time,  adding  when  East 
and  subtracting  when  West;  the  result  will  be  the  M.T.S. 

Take  from  the  Nautical  Almanac,  page  2  of  the  month,  abreast 
of  the  Greenwich  date,  the  sidereal  time,  and  correct  it  for  the 
G.M.T.  by  using  Table  3,  Nautical  Almanac. 

Add  this  corrected  sidereal  time  to  the  M.T.S.  and  subtract  from 
the  sum  the  star's  right  ascension ;  the  result  will  be  the  hour-angle 
of  the  star  West  of  the  meridian. 

If  the  result  is  greater  than  12  hours,  subtract  it  from  24  hours, 
and  the  remainder  will  be  the  hour-angle  of  the  star  East  of  the 
meridian.  If  greater  than  24  hours,  reject  24  hours,  and  the  hour- 
angle  will  be  West  of  the  meridian.  If  it  is  less  than  12  hours,  the 
result  is  the  hour-angle  West  of  the  meridian. 

The  star's  declination  and  right  ascension  must  be  taken  from 
the  star-list  given  in  the  Nautical  Almanac. 


To  Use  the  Azimuth  Tables. — If  the  star's  declination  is  not 
greater  than  23°,  the  azimuth  tables  given  for  the  sun  must  be 
used  in  the  following  manner : 

Always  read  the  H.A.  from  the  p.m.  side  of  the  page,  no  matter  if 
it  is  East  or  West  of  Meridian;  but  if  the  declination  is  greater 
than  23°,  it  will  be  found  in  a  table  published  for  the  purpose  by 
the  United  States  government.  In  this  table  will  be  found  declina- 
tions ranging  from  24°  to  70°,  inclusive,  and  latitude  from  0°  to 
70°,  either  North  or  South.  In  the  latter  table  the  hour-angles 
may  be  taken  from  either  the  right  or  the  left  hand  side  of  the  page. 
Care  should  be  taken,  however,  to  read  the  rules  for  naming  thfl 
azimuths  given  at  bottom  of  each  page. 

If  there  is  any  doubt  about  naming  the  true  azimuth  of  the 
star,  take  the  sextant  and  measure  the  altitude;  then,  if  it  is  rising, 
name  it  East,  but  if  falling,  name  it  West. 


Example.— l^U,  May  21st,  a.m.  at  ship,  a  chron.  showed  10"^  lO'" 
35*  G.M.T.,  when  the  obs.  az.  of  Altair  was  S.  80°  E.  and  var  10° 
40'  E.,  the  ship  being  in  lat.  27°  N.  and  long.  146°  W.  Required  the 
deviation  of  the  compass  for  the  direction  of  ship's  head  at  time 
of  observation. 


I)  KV  [AT  I  OK. 

193 

Ast.  G.M.T.  May 

M.T.S. 

Sid.  T.G.M.  noon 

Red.  from  Table  3, 

20<i  22"  19'" 
-  9    44 

-12    35 

+  3    52 

N.A.                 3 

35^ 
00 

~35 
31 
39 

incre 
H.A. 

Long.  146°  W 
4 

60)584 

9"  44"' 

R.A.  of  mer. 
R.A.  of  star 

16    31 
-19    45 

45 
37 

?ased  by  24  hours. 

20    46 
24    00 

08 

,  West  of  mer. 

14^ 


H.A.  East  of  mer. 


H.A.  3"  14'" 
Lat.  27°  N. 
Decl.  8^°  N. 


N.  102°  36'  E.  because  H.A.  is  E.  of  meridian 
180 

S. 


.„     .7    24  E.  T.  az. 

10    40  E.  allowed  left 

S.     88    04  E.  mag.  az. 
S.     80    00   E.  comp.  az. 

Dev.^    4'  W. 

Examples  for  rractice. 

1894,  June  14tli,  midnight  at  ship,  in  lat.  25°  S.  and  long.  44° 
48'  W. ;  a  chron.  showed  3^  24^"  00^  M.T.G.,  when  the  obs.  az.  of 
the  star  Spica  was  S.  60°  20'  W.;  var.  12°  10'  E.  Required  tlie 
deviation  of  the  compass  for  the  direction  of  ship's  head  at  time  of 
observation. 

Ansicer.—U.A.  4"  39"';  T.  az.  S.  88°  40'  W.:  dev.  l(i°  10'  E. 

1894,  January  27th,  a.m.  at  ship,  in  lat.  37°  S.  and  long.  50°  7' 
W. ;  a  chron.  showed  5"  0°^  00^  G.M.T.,  when  the  obs.  az.  of  Arc- 
turus  was  N.  45°  E. ;  var.  8°  40'  E.  Required  the  deviation  of 
the  compass  for  the  direction  of  ship's  head  at  time  of  observation. 

Answer.— U.A.W  oS-"  or  4"  5"';  T.  az.  X.  5(i°  30' E.;  dev.  2° 
50'  E. 

1894,  May  20th,  v.u.  at  ship,  in  lat.  27°  N.  and  long.  151°  44' 
W. ;  a  chron.  showed  5^  SS""  00^  G.M.T.,  when  the  obs.  az.  of  Procy- 
on  was  S.  5G°  15'  W. ;  var.  13°  20'  E.  Required  the  deviation  of  the 
compass  for  the  direction  of  ship's  head  at  time  of  observation. 

Answer.— ll.A.  3"  50'^':  T.  az.  S.  79°  23'  W. :  dev.  9°  48'  E. 


Taylor's  Mod.  Nav. 


194  Taylok's  Modern  Xavigatiox. 

^TAPIEE'S  DIAGRAM 

A  Method  of  Ascertaining  the  Deviation,  of  the  Compass. 

Considering  the  great  practical  value  of  this  method,  it  is  a 
wonder  that  it  is  not  more  generally  used,  for  with  it  not  only  is 
the  deviation  determined,  but  courses  may  be  set  or  corrected,  and 
compass  bearings  also,  before  plotting  them  on  a  chart. 

The  method  is  not  new,  for  the  author  used  it  himself  at 
least  twenty  years- ago,  and  finds  it  very  useful  even  at  the  present 
time,  especially  when  the  sun  is  obscured  and  azimuths  not  obtain- 
able, the  ship  being,  of  course,  in  sight  of  land. 

As  a  case  in  point,  to  show  the  extreme  usefulness  of  the  method, 
we  will  suppose  a  master  newly  appointed  to  command  a  new  or 
strange  vessel,  and  owing  to  cloudy  weather,  and  the  sun  not  being 
visible,  he  is  not  able  to  determine  the  deviation  of  his  standard 
compass  by  azimuths.  The  question  then  is.  Should  he  proceed  to 
sea  in  ignorance  of  the  deviation,  and  run  the  risk  of  losing  his 
vessel?  He  ought  not  to;  but  I  am  sorry  to  say  there  have  been 
many  instances,  to  my  own  personal  knowledge,  of  masters  putting 
to  ,&'ea,  totally  ignorant  in  regard  to  the  deviation  of  the  ship's  stan- 
dard compass,  because  they  have  never  taken  the  trouble  to  learn 
this  valuable  method.  It  is  hardly  necessary  to  state  that  such 
an  act  on  the  part  of  a  shipmaster  is,  to  say  the  least,  criminal  in 
the  extreme,  as  the  safety  of  the  lives  on  board  and  of  the  property 
intrusted  to  his  care  is  jeopardized  from  his  ignorance  of  the  com- 
pass error. 

It  is  hoped  that  the  student,  after  reading  the  above,  will  give 
special  attention  to  the  following,  but  I  wish  him  thoroughly  to 
understand  that  the  deviations  by  azimuths  or  amplitudes  are 
much  to  be  preferred,  if  it  is  possible  to  obtain  them.  The  reason 
of  this  will  be  more  fully  explained  under  the  heading  of  "Com- 
pass-Adjustment." 

Description  of  tlic  Diagram. 

The  diagram  represents  the  edge  of  a  compass-card  cut  off  and 
straightened  out,  with  certain  lines  passing  througli  each  point  at 
an  angle  of  60°. 

If  the  student  will  examine  the  accompanying  diagram  he  will 
see  that  the  top  part  begins  at  N.XW.,  then  North.  N.XE.,  Ts^N.E., 
and  so  on  until  at  the  bottom  will    l)e    found    JST.XK-;    iin<^    '^^- 


Deviation.  19-^ 


though  there  are  really  only  3:^  points  of  the  eompass  on  the  dia- 
gram, it  will  be  noticed  that  there  are  two  in  excess— one  at  the 
top  and  one  at  the  bottom.  This  is  for  convenience'  sake  when 
drawing  the  curve. 

The  lines  running  across  the  diagram  have  special  meanings; 
thus,  the  dotted  lines  represent  compass  courses,  and  plain  lines  cor- 
rect magnetic  courses.  This  is  a  very  important  matter  for  the 
student  to  remember,  as  will  eventually  be  seen. 

Having  inspected  the  diagram,  we  will  now  proceed  with — 
How  to  Handle  a  Ship  and  Put  the  Method  into  Actual  Practice. 

Have  ship  upright.  Slow  the  engines  so  that  the  ship  has  sim- 
ply steerage-way,  for  the  reason  that  the  smaller  the  circle  the  ship 
describes,  the  better  will  be  the  result. 

Select  some  distant  stationary  object,  like  the  top  of  a  moun- 
tain, a  large  tree,  or  a  house  on  the  shore,  or  any  other  distinct 
distant  object;  the  more  distant,  the  better. 

Steady  the  ship's  head  on  Xorth  and  take  a  bearing  of  the  dis- 
tant object  by  the  standard  compass  or  Pelorus ;  mark  this  bearing 
abreast  of  Xorth. 

Next  steady  her  head  on  X.E.  and  take  another  bearing,  and 
mark  it  down  abreast  of  N.E. 

Next  steady  her  head  East  and  take  another  bearing,  and  mark 
it  abreast  of  East,  repeating  the  operation  for  every  four  points; 
we  shall  then  have  eight  bearings,  and  the  mean  of  them  all  will 
be  the  correct  magnetic  bearing  of  the  distant  object. 

To  Find  the  Correct  Magnetic  Bearing. 

First  Case. — If  all  the  bearings  have  the  same  name,  add  them, 
and  divide  the  sum  by  8 ;  the  result  will  be  the  correct  magnetic 
bearing,  of  the  same  name  as  compass  bearings. 

Second  Case. — If  some  bearings  are  from  the  Xorth  and  some 
from  the  South,  read  them  all  from  the  Xorth  or  from  the  South, 
add  them,  and  divide  the  sum  by  8;  the  result  will  be  the  correct 
magnetic  bearing,  to  be  named  the  same  name  as  the  compass  bear- 
ings. 

Third  Case. — If  some  bearings  are  reckoned  to  the  East  and 
some  to  the  West,  take  the  sum  of  the  easterly  bearings  and  the 
sum  of  the  westerlv  I)earino-s.  subtract  the  sum  of  one  from  the 


196  Taylor's  Modern  Xavkjatiox. 

=um  of  the  other,  according  to  which  is  the  greater,  and  divide  the 
difference  by  8;  the  resuh  will  be  the  magnetic  bearing,  to  be 
named  the  same  as  the  greater  sum. 

The  magnetic  bearing  being  found,  we  next  proceed  to  deter- 
mine the  deviation  for  every  fourth  point  of  ship's  head,  thus: 

Take  the  difference  between  the  first  compass  bearing  of  the 
distant  object  and  the  magnetic  bearing;  the  result  will  be  the 
deviation,  to  be  named  East  if  the  magnetic  bearing  is  to  the 
right  of  the  compass  bearing,  and  West  if  to  the  left;  mark  this 
deviation  down  abreast  of  Xorth;  repeat  this  for  each  bearing 
taken,  and  we  have  the  deviation  of  the  compass  for  every  four 
points. 

To  Draw  the  Curve. 

With  a  pair  of  dividers  measure  on  the  center  line  of  the  diagram 
the  number  of  degrees  of  deviation  for  ship's  head  ISTorth  by  com- 
pass, then  place  one  leg  of  the  dividers  on  Xorth  and  measure  out 
along  the  dotted  line  to  the  right  if  the  deviation  is  East,  but  to 
the  left  if  West,  and  make  a  mark. 

Xext  measure  on  center  line  the  amount  of  deviation  on  X.E. 
by  compass,  and  with  one  foot  of  the  dividers  on  X.E.  measure  out 
on  the  dotted  line  again  and  make  another  mark;  repeat  this  for 
every  four  points,  with  the  deviation  on  Xorth  marked  at  the  bot- 
tom of  diagram  as  well  as  at  the  top. 

Through  all  of  the  positions  marked  on  diagram  draw  a  flowing 
curve,  always  from  the  center  line,  not  towards  it;  the  result  is 
termed  a  curve  of  deviation.  From  it  a  table  of  deviations  may  be 
made  for  each  and  every  point  and  quarter-point,  if  desired,  not 
only  for  deviation  ship's  head  l)y  compass,  but  also  deviation  for 
ship's  head  magnetic. 

To  make  a  table  of  deviations  for  ship's  head  by  compass  for 
every  point,  place  one  leg  of  the  dividers  on  X.XE.  and  measure 
out  along  the  dotted  line  to  the  curve,  then  lay  the  dividers  on 
center  line  and  note  the  nunilxT  of  degrees  contained  between  the 
legs  of  the  dividers;  this  will  be  the  deviation  on  X.XE..  to  be 
named  East  if  the  curve  is  to  the  right  and  West  if  to  tlic  left  of 
the  center  line,  according  to  the  printed  instructions  at  top  of 
diagram. 
*  "  Xext  place  one  leg  of  tlie  dividers  on  X.X.K.  and  n\ensure  out  on 
the  dotted  line  to  the  curve  again,  and  find  the  deviation  as  be- 
fore, then  repeat  for  every  point,  and  mark  the  same  on  a  card. 

To  find  ilie  deviation  of  tlie  (-(nnpass  for  every  point  of  ship's 


^(Ty 


jjait  ui  LiiL'  ei^juer  ime  roproscntino-  the  bcavino-.  and  if  the  devia- 
tion is  East,  measure  down  the  line,  l)ut  if  We>t,  nibasiire  np  the 


196  Taylor's  Modern  Xavigatiox. 

jiim  of  the  other,  according  to  which  is  the  greater,  and  divide  the 
difference  by  8;  the  resnh  will  be  the  magnetic  bearing,  to  be 
named  the  same  as  the  greater  sum. 

The  magnetic  bearing  being  found,  we  next  proceed  to  deter- 
mine the  deviation  for  every  fourth  point  of  ship's  head,  thus: 

Take  the  difference  between  the  first  compass  bearing  of  the 
distant  object  and  the  magnetic  bearing;  the  result  will  be  the 
deviation,  to  be  named  East  if  the  magnetic  bearing  is  to  the 
right  of  the  compass  bearing,  and  West  if  to  the  left;  mark  this 
deviation  down  abreast  of  ISTorth;  repeat  this  for  each  bearing 
taken,  and  we  have  the  deviation  of  the  compass  for  every  four 
points. 

To  Draw  the  Curve. 

With  a  pair  of  dividers  measure  on  the  center  line  of  the  diagram 
the  number  of  degrees  of  deviation  for  ship's  head  North  by  com- 
pass, then  place  one  leg  of  the  dividers  on  Xorth  and  measure  out 
along  the  dotted  line  to  the  right  if  the  deviation  is  East,  but  to 
tbe  left  if  West,  and  make  a  mark. 

Xext  measure  on  center  line  the  amount  of  deviation  on  X.E. 
by  compass,  and  with  one  foot  of  the  dividers  on  X.E.  measure  out 
on  the  dotted  line  again  and  make  another  mark;  repeat  this  for 
every  four  points,  with  the  deviation  on  Xorth  marked  at  the  bot- 
tom of  diagram  as  well  as  at  the  top. 

Through  all  of  the  positions  marked  on  diagram  draw  a  flowing 
curve,  always  from  the  center  line,  not  towards  it;  the  result  is 
termed  a  curve  of  deviation.  From  it  a  table  of  deviations  may  be 
made  for  each  and  every  point  and  quarter-point,  if  desired,  not 
only  for  deviation  ship's  head  by  compass,  but  also  deviation  for 
ship's  head  magnetic. 

To  make  a  table  of  deviations  for  ship's  head  by  compass  for 
every  point,  place  one  leg  of  the  dividers  on  X.XE.  and  measure 
out  along  the  dotted  line  to  the  curve,  then  lay  the  dividers  on 
center  line  and  note  the  numlHT  of  degrees  contained  between  the 
legs  of  the  dividers;  this  will  l)e  the  deviation  on  X.XE..  to  be 
named  East  if  the  curve  is  to  the  right  and  West  if  to  tlie  left  of 
the  center  line,  according  to  the  printed  insti'iu-tions  at  top  of 
diagram. 
*  '  Xext  place  one  leg  of  tlie  dividers  on  X.X.P'.  and  nicasiire  out  on 
the  dotted  line  to  the  curve  again,  and  find  tlie  deviation  as  be- 
fore, then  repeat  for  every  point,  and  mark  the  same  on  a  card. 

To  find  the  deviation  of  the  compass   for  every  ])nint  of  ship's 


jorc 


(ind   tlic  .li 


)f  tl 


for  cxcrv 


Deviation.  191 


head  magnetic,  measure  out  on  tlie  plain  line  instead  of  dotted 
lin-. 

The  curve  being  drawn  neatly,  we  will  now  explain  how  to  find 
a  course  to  steer  by  compass,  and  also  how  to  correct  a  course 
actually  steered. 

First  Case. — Suppose  a  magnetic  course  is  taken  from  a  chart, 
and  the  compass-course  is  required. 

On  the  center  line  find  the  magnetic  course  and  place  one 
leg  of  the  dividers  on  it,  then  measure  out  to  the  curve  on  or 
parallel  to  a  plain  line,  keep  the  leg  on  the  center  line  stationary 
and  sweep  with  the  other  back  to  the  center  line  in  the  same 
direction  as  the  dotted  line  runs,  and  where  it  touches  the  center 
line  will  be  the  course  to  steer  by  compass  to  make  the  magnetic 
course  taken  from  the  chart. 

A  little  rhyme  to  assist  the  memory  in  regard  to  the  above: 

"If  you  seek  to  steer  a  course  allotted. 
Go  out  by  the  plain  and  come  back  by  the  dotted." 

Second  Case. — Suppose  a  course  is  being  steered  by  a  compass 
and  the  magnetic  course  the  ship  is  making  is  required ;  proceed 
as  follows : 

On  the  center  line  find  the  compass  course,  place  one  leg  of  the 
dividers  on  it  and  measure  out  to  the  curve  on  or  parallel  to  a 
dotted  line,  keep  the  leg  on  the  center  line  stationary  and  with 
the  other  sweep  back  to  the  center  line  in  the  same  direction  as  the 
plain  line  runs,  and  where  it  touches  will  be  the  magnetic  course  the 
ship  is  making  good. 

There  is  a  rhyme  for  this,  also: 

"From  a  compass  course  a  magnetic  course  to  gain, 
Go  out  by  the  dotted  and  come  back  by  the  plain." 

To  correct  bearings  taken  by  tlie  compass  before  laying  the 
same  on  a  magnetic  chart,  note  the  direction  of  ship's 
head  at  time  of  taking  the  bearing  and  find  it  on  the  center 
line;  measure  out  to  the  curve  on  or  parallel  to  a  dotted  line; 
this  will  give  the  deviation  for  whatever  the  ship  was  heading  at 
the  time.  With  this  space  in  the  dividers  place  one  leg  on  that 
part  of  the  center  line  representing  the  bearing,  and  if  the  devia- 
tion is  East,  measure  down  the  line,  but  if  We>t,  measure  up  the 


198 


Taylor's  ]\Iodekx  Xavigatiox. 


Hue,  and  where  the  second  leg  touches  the  center  line  will  be  the 
magnetic  bearing  to  la}-  on  a  chart. 

For  downright  handiness  this  ]nethod  is  hard  to  beat,  but,  be  it 
remembered,  it  is  of  use  only  to  coasting-vessels  having  a  compara- 
tively short  run  from  port  to  port.  If  the  vessel  is  navigating  be- 
tween ports  widely  separated  as  to  geographical  position,  recourse 
must  be  had  to  the  taking  of  azimuths  continually.  Although  the 
diagram  is  especially  intended  to  be  used  when  the  sun  is  not  visible, 
it  may  not  be  amiss  to  state,  before  concluding  this  article,  that  it 
may  be  used  at  other  times,  thus: 

Supposing  the  ship  to  be  at  sea  and  the  weather  clear,  steady 
the  ship's  head  on  every  four  points  of  the  compass  and  determine 
the  deviation  on  them  by  azimuths,  plot  the  results  on  the  diagram 
as  before  and  draw  a  curve. 

This  is  really  a  much  better  method  than  taking  a  bearing  of 
the  land,  because  of  its  being  possible  to  steady  the  ship  longer  on 
a  course,  whereas  when  taking  a  bearing  of  the  land  it  is  of  the 
utmost  importance  for  the  ship  to  make  as  small  a  circle  as  possible. 

The  following  problem  is  illustrated  by  the  thicl:  hlack  curve  on 
ihe  diagram : 


Ship's?  Head, 

bv  Standard 

Compass. 

Bearing;  of   Dis- 
tant Object. 

Deviation. 

Sliip's  Head, 

by  Sta-  dard 

Compass. 

Bearing  of    Dis- 
tant Objeot. 

Deviati  .n. 

N. 

N.E. 
E. 
S.E. 

s.  50°  ^y. 

S.  54°  W. 
S.  59°  W. 
S.  68°  W. 

20°  E. 

16°  E. 

11°  E. 

2°  E. 

s. 

s.w. 

w. 

N.W. 

S.  79°  W. 
S.  87°  W. 
8.  90°  W. 

s.  7r  w. 

9°  W. 
17°  W. 
20°  W. 

1°  W. 

S.  231°  W. 
S.327   W. 

8.  827°  \V. 

8)558 

S.  69°  6'     Call  tliis  S.  70°  W.,  liecause  it  is  nearer  to 
70°  than  69°     Correct  magnetic  bearing  S.  70°  W. 


S,59°W.     S.  68°W. 
S.  70°  W.     S.  70°  W. 
20°E.forN.;  1()°  E.forN.E.;  11°E.  for  E.;  2°  E.  for  S.E. 


Devivtiox.  199 


Comp.-  j  j^_^yo^y_        S.87°W.  S.90°W 

bearings  ) 


S.71°  W, 


^^^''^-  j  S.70°  W.   S.  70°  W.    S.  70°  W.   S.70°  W 


bearing 


9°  \V.  for  S.;  17°  W  for  S.W.;  20°  Wfor  W.;   1°  W. 
for  N.W. 


To  Construct  the  Dcciatioii  Curve  on  tlie  Diagram. — The  devia- 
tion for  ship's  head  on  North  is  20°  E.  Measure  20°  on  the  cen- 
ter line,  and  place  one  leg  of  the  dividers  on  North  and  the  other 
on  the  dotted  line,  passing  through  North  to  the  right,  and  make  a 
mark. 

Then  take  the  deviation  for  N.E.,  which  is  16°  E.  Measure  16° 
on  the  center  line,  and  place  one  leg  of  the  dividers  on  N.E.  and 
the  other  on  the  dotted  line,  passing  through  N.E.  to  the  right, 
and  make  a  mark. 

Then  measure  the  deviation  for  East  and  S.E.  in  the  same  man- 
ner, but  when  laying  off  the  deviation  for  South  and  S.W.,  West 
and  N.W.,  measure  to  the  left  of  the  center  line  because  the  devia- 
tions on  those  points  are  westerly.  Eight  deviations  being  then 
laid  on  the  diagram,  the  curve  can  now  be  drawn. 

Take  your  pencil  and  draw  a  flowing  curve  very  carefully 
through  all  of  these  marks. 

In  drawing  the  curve  by  hand  you  must  be  very  careful,  as  not 
one  man  in  a  dozen  can  do  it  at  first  with  any  degree  of  accuracy. 

The  best  way  is  to  use  a  wooden  parabolic  curve,  or  a  piece  of 
flexible  whalebone,  and  with  the  assistance  of  either  of  these  the 
curve  may  be  drawn  more  accurately  than  by  hand. 

To  Find  a  Compass  Course  to  Steer  from  a  Magnetic  Course. — 
Look  for  the  magnetic  course  on  the  center  line,  then  go  out  from 
the  center  line  to  the  curve  on  or  parallel  to  a  plain  line,  and  re- 
turn to  the  center  line  on  or  parallel  to  a  dotted  line.  The  point 
returned  to  on  the  center  line  will  be  the  course  to  steer  by  standard 
compass. 

Example. — W.XN^N.  magnetic,  to  find  compass  course  to 
steer. 

Look  on  the  center  line  for  W.XN.i/^N.;  lay  the  parallel  rulers 
along  the  nearest  plain  line;  move  the  rulers  until  the  edge  is  ex- 


200  Taylor's  ^Modekx  Xavigatiox. 


iictly  over  W.X^-V2^;  and  draw  a  line  from  it  to  the  curve;  now 
lay  the  rulers  over  the  nearest  dotted  line  and  move  them  over  to 
that  part  of  the  curve  cut  by  the  first  line;  then  draw  a  line  back 
to  the  center  line,  and  where  the  last  line  cuts  the  center  line  will 
be  the  compass  course  to  steer. 

Ansiver.—'N.  62  ^^r  W. 

It  is  not  necessary  to  draw  lines;  the  magnetic  course  may  be 
found  by  sweeping  with  the  dividers,  as  explained  in  a  previous 
rule. 

Examples  for  Practice. — Magnetic  courses,  to  find  the  compass 
courses. 

1:  S.W.XS.     2:  N.XW.  3:  S.  15°  E. 

4:  N.N.E.        5:  N.E.XE.  6:  N.  72"  E. 

Afisivers. 

1:  S.  52°  W.  2:  N.  24°  W.  3:  S.    8°  E. 

4:  N.    3°  E.    5:  N.  40°  E.  6:  N.  57°  E. 

To  Find  the  Magnetic  Course  from  a  Compass  Course  Steered. — 
Look  for  the  cojnpass'  course  on  the  center  line,  and  go  out  from 
this  center  line  to  the  curve  on  or  parallel  to  a  dotted  line,  and 
return  to  the  center  line  on  or  parallel  to  a  plain  line.  The  point 
arrived  at  on  the  center  line  will  be  the  magnetic  course. 

^xam/j/f.— Suppose  you  had  steered  S.  52°  W.  by  compass,  and 
you  wish  to  find  the  magnetic  course  made  good. 

Look  on  the  center  line  for  S.  52°  W.;  lay  the  rulers  along  the 
nearest  dotted  line,  and  move  them  over  to  S.  52°  W.,  and  draw  a 
line  towards  the  curve;  then  lay  the  rulers  along  a  plain  line  and 
move  them  until  they  are  over  that  part  of  the  curve  cut  by  the 
first  line,  and  draw  a  line  back  to  the  center  line.  The  point  arrived 
at  on  the  center  line  will  be  tlie  magnetic  course  made  good. 

Ansivcr.—S.W.X^- 


Examples  for  rrarlice. 

— CNnnpass  com 

•sfs.  to  find  the  magnetic 

courses. 

1:   W.XS. 

2:  S.S.W. 

3:  S.E.XS. 

4:  East 

5:  E.N.E. 

Answers. 

6:  N.E.XN. 

1:  S.  59°  W. 

2:  S.    9°  W. 

3:  S.E.XS. 

4:  S.  79°  E. 

5:   N.  82°  E. 

6:  N.  51°  E. 

J)i;\  lAiioN. 


201 


To  Correct  Conipass  licdriiigs  to  Find  Magnetic  Bearings. — 
Xote  the  direction  of  the  sliip's  head  at  the  time  of  taking  the 
bearing.  Look  for  the  direction  of  the  ship's  head  on  the  center 
line  and  measure  from  it  to  the  curve  along  a  dotted  line  with  the 
dividers;  then  lay  the  dividers  on  the  center  line,  and  you  will 
have  the  degrees  of  deviation,  East  if  the  curve  is  to  the  right, 
and  West  if  it  is  to  left.  Apply  this  deviation  to  the  bearings 
taken,  allowing  East  to  the  right  and  West  to  the  left;  the  result 
will  be  the  magnetic  bearing.  The  same  result  is  atlained  by  a 
previous  rule. 

Exnwple. — Ship's  head  N.  E.  by  compass,  bearing  S.  W.  Re- 
quired the  correct  magnetic  bearing. 

Measure  from  X.E.  along  the  dotted  line  to  the  curve ;  then  lay 
the  dividers  on  the  center  line,  and  you  will  find  that  you  have  17° 
E.  deviation,  because  the  curve  is  to  the  right;  apply  this  17°  E. 
deviation  to  the  right  of  the  bearing  and  you  will  get  S.  61°  W. 
magnetic. 

Examples  for  Practice. 

Magnetic 
Ship's  Head.     Bearings.       Bearings. 
S.E.XE.  N.N.E.         N.  28°  E. 

N.N.W.  S.W\XS.     S.    47°  W. 

S.XE.  W.4S.  S.   78°  \V. 

W.N.W.  N.4E.  N.     8°  W. 

The  folhiwing  problem  is  illustrated  by  the  red  curve  on  the 
diagram. 


Ship's   Head 

by  Standard 

Compass. 

Bearing  of  Dis- 
tant Object. 

Deviation. 

Ship's  Head 

by  Standard 

Compass. 

Bearing  of   Dis- 
tant Object 

Deviation. 

N. 

N.E. 
E. 
S.E. 

S.  85°  E. 
N.  85°  E. 
S.  80°  E. 
S.  69°  E. 

164°  E. 

264°  E. 

ll|°  E. 

0^°  E. 

s. 

s.w. 

w. 

N.W. 

S.  52°  E. 
S.  41°  E. 
S.  57°  E. 
S.  69°  E. 

164°  W. 

274°  W. 

114°  W. 

04°  E. 

Com 
Mag. 

S. 329°  E. 
S.219°E. 

mag.  bearing. 

.  85°    E.             S.  95°     E. 
.  684°  E.             S.  684°  E. 

8)548 

S.    68i°  E 

X -bearings  S 
bearings     S 

164°  E.  for  N.      26^°  E.  for  N.  E. 


202  Taylor's  Modern  Xavigatiox. 


Comp.-bearings  S.  80°    E.  S.  69°    E. 

Mag.  bearings     S.  68^°  E.  S.  68^°  E. 

ni°  E.  for  E.         0^°  E.  for  S.  E. 

Comp.-bearings  S.  52°    E.  S.  41°    E. 

Mag.  bearings     S.  68^°  E.  S.  68^°  E. 

16"^°  W.  for  S.      27i°  W.  for  S.  \V. 

Comp.-bearings  S.  57°    E.  S.  69°    E. 

Mag.  bearings     S.  68^  E.  S.  68^°  E. 

lli°  W.  for  W.     00^^°  E.  for  N.  W. 

In  this  case  the  bearings  have  not  all  the  same  names,  but  we 
make  them  of  the  same  name  by  reckoning  them  all  from  the 
South.    Note  that  N.  85°  E.  is  S.'  95°  E. 


Examples. — Given   correct   magnetic   courses,    to   find   compass 
courses. 

1:  N.N.E.  2:  S.XW.  3:  W.^  S. 

Answers. 
1:  N.  4°  E.        2:  S.  37°  W.      3:  N.  85°  W. 

Examples. — Given  compass  courses,  to  find  correct  magnetic 
courses. 

1:  N.E.XE.      2:  West  3:  W.XN. 

Answers. 
1:  N.  81°  E.      2:  S.  78°  W.     3:  N.  88°  W. 

Examples. — Ship's  head  E.X.E. ;  bearings  of  two  distant  objects 
by  compass  X.W.XW.  and  E.XX.  Find  the  correct  magnetic 
bearings. 

N.W.XW.  =  N.  e56°  W.  E.XN.  =  N.      79°  E. 

Dev.  21    E.  Dev.      21    E. 

Cor.  mag.  N.  35°  W.  N.    100°  E. 

180 

Cor.  mag.  S.^0°  E. 

The  following  probknu  is  illustrated  by  the  ihin  hlacJc  curve  on 
the  diagram. 


Dkviat[ox. 


203 


Ship's  Head, 

by  StandarC. 

Compass. 


N. 

N.E. 
E. 

S.E. 


Huarmgs  o 
taut  Objc 


Ship's  Head, 
Deviation,    by   Standard 
Compass. 


S.  22°  W. 
S.  48°  W. 
S.  56°  W. 
S.  45°  W. 


3°  E. 
23°  W. 
31°  W. 
20°  W. 


S. 

s.w. 
w. 

N.W 


Bearings^  of  Dis-     Deviation, 
tant  Object. 


S.  29°  W 

S.  2°  E. 
S.  6°  E. 
S.    8°  W.      17°  E 


4°  W. 
27°  E. 
31°  E. 


The  sum  of  the  S.W.  bearings  is  8.  208°  W. 
The  sum  of  the  S.E.  bearings  is  S.      8°  E. 

8)200 
Cor.  mag.  bearing,  S.  25°  W. 


Comp.-bearings  S.  22°  W. 
Mag.  bearings     S.  25°  \V. 

Dev.       3°  E.  on  N. 


Comp.-bearings  S.  56°  W. 
Mag.  bearings     S.  25°  W. 

Dev.     31°  W. 


E. 


Comp.-bearings  S.  29°  W. 
Mag.  bearings     S.  25°  W. 

Dev.         4°  W.  on  S. 

Comp.-bearings  S.    6°  E. 
Mag.  bearings      S.  25°  W. 

Dev.     31°  E.  on  W. 


s. 
s. 

48° 
25° 

W. 

w. 

23° 

w. 

on 

N.E. 

s. 
s. 

45° 
25° 

w. 
w. 

20° 

w. 

on 

S.E. 

s 

2° 
25° 

E. 
W 

27° 

E. 

on 

S.W. 

s 
s 

8° 
25° 

T7^ 

W 
W 

E. 

on 

N.W 

In  this  case  some  of  the  bearings  are  westerly  and  some  easterly, 
so  we  add  all  the  westerly  together  and  all  the  easterly  together 
and  subtract  the  lesser  sum  from  the  greater  and  divide  the  re- 
mainder by  8.  The  result  is  the  correct  magnetic  bearing  of  the 
distant  object,  to  be  named  the  same  as  the  greater. 


Examples. — Given  magnetic  courses,  to  find  compass-courses. 

1:  N.E.XN.      2:  E.S.E.  3:  W.  2°  S. 

Answers. 
1:   N.  61°  E.      2:  S.  47°  E.        3:  S.  58°  W. 


204 


Taylor's  !Moderx  Xavigatiox. 


Examples. — Given  compass  courses,  to  find  magnetic  courses. 

1:  N.XE.         2:  W.XN.  3:  S.W.i  W. 

Ansicers. 
1:  N.  7°  E.      2:  N.  51°  W.      3:  S.  79°  W. 

Example. — Ship's  head  S.W.XW.;    compass    bearings    of    two 
distant  objects  W.VoS.  and  X.i/^E.    Find  correct  magnetic  bearings, 

Ansivers. 
N.  65°  E.  N.  36^°  E. 


Deviation  hy  Napier  s  Dingram. 

Example. — In  the  following  table  give  the  correct  magnetic  bear- 
ing of  the  distant  object  and  thence  the  deviation. 


Ship's    Head 

by  Standard 

Compass. 

Bearing  of    Dis- 
tant Object 
by  standard 
Compass. 

Deviation 
Required. 

Ship's    Head 

by  Standard 

Compass. 

Bearing    of  Dis- 
tant Object 
by   Standard 
Compass. 

Deviation 
Required. 

North  .  . . 

N.  E  . . . . 
East  .... 
S.  E 

N.  80°  E .  . . 

South  .  .  . 
S.  W.... 

West.... 
N.  W.    .  . 

N.  63°  E 

N.  87°  E.  .. 

N.  43°  E 

N.  85°  E.  . 

N.  55°  E 

N.  82°  E.  .  . 

N.  70°  E 

From  the  above  table  construct  a  Xapier's  curve,  and  give  the 
courses  you  would  steer  b}'  standard  compass  to  make  the  following 
courses  correct  magnetic : 

Correct  magnetic  courses,  X.E.X^""-,  E.S.E.,  S.XW.,  S.W. 

Compass  courses, 

Suppose  you  steer  the  following  courses  by  standard  compass, 
find  the  correct  magnetic  courses  from  the  curve  drawn : 

Compass  courses,  X.XE..  S.  54°  E..  S.W.XW-  W.X.W. 

Correct  magnetic  courses, 

You  have  taken  the  following  hearings  of  a  distant  oljject  by 
your  standard  compass  as  above.  With  the  ship":^  liead  S.W..  find 
the  correct  magnetic  bearings. 

Compass  bearings.  East  and  S.  '10°  \V. 

An^ivcfs. 

Correct  magnetic  bearing,  N".  70  E. 

Deviations,  10°  W.,  17°  W.,  15°  W.,  12°  W..  7°  E.,  27°  E., 
15°  E. 

Compass  courses.  X.  51°  E.,  S.  54°  E.,  S.  2°  W..  S.  24°  W. 


Deviation. 


20o 


Magnetic  courses,  X.  1°  W..  S.  (iG°  E.,  8.  «1°  W.,  X.  (iO'  W. 
Magnetic  bearings,  S.  G3°  E.,  N.  84°  W. 

Deviatlun  by  A^apier's  Dmgrani. 

Example. — In   the    following   table   give   the   correct    magnetic 
bearing  of  the  distant  object  and  thence  the  deviation. 


Ship's  Head, 

by  Standard 

Compass. 

North.    . 
N.E.    .. 
East  .... 
S.E 

Bearing    of  Dis- 
tant  Object    by 
standard     Com- 
pass. 

Deviation 
Required. 

Ship's  Head, 

by  Standard 

Compass. 

Bearing  of  Dis- 
tant   Object    by 
Standard     Com- 
pass. 

Deviation 
Required. 

N.  88°  W. 

South  .  .  . 

S.W 

West.  .  .  . 
N.W 

S.  87°  W. 

N.  67°W... 

N.  60°  W. 

S.  66°  W. .  . 
S.  54°  W. 

N.  66°  W. . . 

S.  70°  W. .  . 

From  the  above  table  construct  a  Xapier's  curve,  and  give  the 
courses  you  would  steer  by  standard  compass  to  make  the  following 
courses  correct  magnetic : 

Correct  magnetic  courses,  X.E.XE.,  S.E.,  W.S.W. 

Compass  courses. 

Suppose  you  steer  the  following  courses  by  standard  compass, 
find  the  correct  magnetic  courses  from  the  curve  drawn : 

Compass  courses,  East,  S.S.E.,  W.XS. 

Correct  magnetic  courses, 

You  have  taken  the  following  bearings  of  a  distant  object  by 
3^our  standard  compass  as  above.  With  the  ship's  head  S.W.XW. 
^/-oW.,  find  the  correct  magnetic  bearings. 

Compass  bearings,  E.XS.  and  Xorth. 


A II  steers. 

Magnetic  bearing,  X.  90°  W.  or  West. 
Deviations,  2°  W.,  23°  W..  30°  W..  24°  W.,  3°  E..  24°  E., 
20°  E. 

Compass  courses,  X.  86°  E.,  S.  29°  E.,  S.  43°  W. 
Magnetic  courses,  X.  60°  E.,  S.  35°  E..  X.  66°  W. 
Magnetic  bearings,  S.  47°  E..  X.  31°  E. 


16°  E. 


Deviation  hi/  Napier's  Diagram. 

Example. — In   the  following  tahk-  give  the    correct 
bearing  of  the  distant  object  and  thence  the  deviation. 


masrnetie 


206 


Taylor's   Mooekx    Xavigatiox. 


Ship's    Head 

by  Standard 

"Compass. 


North 
N.  E. 
East  . 
S.  E.. 


Bearing  of    Dif 

tant  Object 

by  Standard 

Compass, 


N. 10°  W 
N.    6°W 
N.  12°  E, 
N.  20°  E . 


Ship's  Head 
Deviation  'by  Standard 
Required.       Compass. 


South 
iS.  w. 

I  West. 

N.W. 


Bearing  of  Dif 

tantObjcLt 

by  Standard 

"Compass. 


N.  3°  E. 
N.  20°  W 
N.  18°  W 

N.  12°  W 


Deviation 
Required. 


From  the  above  table  construct  a  Xapier's  curve,  and  give  the 
courses  you  would  steer  by  standard  compass  to  make  the  following 
courses  correct  magnetic : 

Correct  magnetic  courses,  E.XN.y2N.,  S.S.E.,  West. 

Compass  courses, 

Suppose  you  steer  the  following  courses  by  standard  compass,, 
find  the  correct  magnetic  courses  from  the  curve  drawn : 

Compass  courses,  S.E.>4E.,  W.S.W.,  N.W. 

Correct  magnetic  courses. 

You  have  taken  the  following  bearings  of  a  distant  object  by 
your  standard  compass  as  above.  With  the  ship's  head  E.XS.,  find 
the  correct  magnetic  bearings. 

Compass  bearings,  S.E.  and  S.W. 

Answers. 

Correct  magnetic  bearing,  N.  4°  W. 

Deviations,  6°  E.,  2°  E.,  16°  W.,  24°  W.,  ?°  W.,  16°  E.,  14°  E.,. 
8°  E. 

Compass  courses,  N.  88°  E.,  S.  10°  E.,  S.  '13°  W. 
Magnetic  courses,  S.  74°  E.,  S.  85°  W.,  N.  36°  W. 
Magnetic  bearings,  S.  64°  E.,  S.  26°  W. 


Deviation  by  Napier  s  Dlagrafn. 

Example. — In   the   following  table  give   the    correct 
bearing  of  the  distant  object  and  thence  the  deviation. 


magnetic 


Ship's    Head 

by  Standard 

Compass. 

Bearing;    of     |ii>- 
laiil  ()l.jr,.| 

■(Join  pass. 

Ko.iuiivd. 

Shii.'s    Head 

by   Standard 

Compass. 

Bearing    of   Dis- 
tant Object 
by   Standard 
Comprtss. 

Deviation 
Required. 

North  .  .  . 

N.  E  .    .  . 

East 

S.  E 

N.  13°  E... 

N     9°  E 

South  .  .  . 
S.  W 

N.    8°  W.. '. 

N.    8°  E    

N.  16°  W.  . 

West .... 
N,  W. 

N.  23°  E 

N.  24°  W 

N.  20°  E    .  . 

1 

Deviatiox.  20r 


From  the  above  table  construct  a  Xapier's  curve,  and  give  the 
courses  you  would  steer  by  standard  compass  to  make  the  following 
courses  correct  magnetic. 

Correct  magnetic  courses,  ]N'.  10°  E.,  S.  60°  E.,  S.  80°  W. 

Compass  courses, 

Suppose  you  steer  the  following  courses  by  standard  compass, 
iind  the  correct  magnetic  courses  from  the  curve  drawn : 

Compass  courses,  S.  50°  E.,  S.  15°  E.,  X.  55°  W. 

Correct  magnetic  courses, 

You  have  taken  the  following  bearings  of  a  distant  object  by 
your  standard  compass  as  above.  With  the  ship's  head  S.  40°  E., 
find  the  correct  magnetic  bearings. 

Compass  bearings,  S.  15°  E.  and  X.  75°  W. 

Answers. 

Correct  magnetic  bearing,  X.  3°  E. 

Deviations,  10°  W.,  G°  W.,  19°  E.,  21°  E.,  11°  E..  5°  W., 
20°  W.,  17°  W. 

Compass  courses,  X.  21°  E.,  S.  82°  E.,  X.  80°  W. 
Magnetic  courses,  S.  24°  E.,  S.  4°  W.,  X.  73°  W. 
Magnetic  bearings,  S.  10°  W.,  X.  50°  W. 

Eemarks  ox  t]ie  Fixdixg  of  the  Deviatiox. 

The  methods  given  in  this  section  to  determine  the  deviation 
are  only  what  every  navigator  deserving  the  name  ought  to  be 
thoroughly  conversant  with ;  for  of  what  value  is  it  to  know  where 
the  ship  is  if  the  correct  course  to  another  place  cannot  be  found? 

There  are,  no  doubt,  many  watch-officers  and  shipmasters  who 
think  that  the  star  and  planet  azimuths  have  no  practical  value, 
and  are  something  so  far  above  the  ordinary  that  it  requires  a 
university  education  to  enable  one  to  master  them ;  but  if  the  navi- 
gator will  only  take  the  trouble  to  investigate,  he  will  find  that  they 
arc  as  easy  and  as  useful  as  azimuths  of  the  sun,  and  at  the  present 
time,  owing  to  the  use  of  so  much  iron  and  steel  in  the  construc- 
tion of  modern  vessels,  and  to  the  installation  of  electric-light 
plants,  star  azimuths  are  an  indispensable  adjunct  of  modern  navi- 
gation, as  the  following  extract  from  the  Army  and  Navy  Register 
will  prove : 


208  Taylok's  Modekx   Navioatiox. 


.  NAVY  DEPARTMENT, 
Special  Order  No.  !). 

Washington,  July  19,  1901. 
The    Department    publishes    for    the    information    and    guidanc-e    of    the 
service  the  following  correspondence  in  regard  to  the  effect  on  the  standard 
compass  of  a  ground  in  the  bridge  electric  circuit: 

BUREAU  OF  EQUIPMENT,  NAVY  DEPARTMENT, 

Washington,  D.  C,  June  15.  1901. 
Sir:    1.  The  Bureau  calls  attention  to  the  inclosed  copy  of  a  letter  re- 
ceived from  the  commanding  officer  of  the  U.  S.  S.  Oregon  on  the  disturb- 
ing effect  on   the   standard   compass   caused  by   a  "ground"   in  the  bridge 
electric  circuit. 

2.  The  incident  is  of  interest  to  the  Bureau  and  of  importance  to  the 
naval  service,  as  it  points  out  a  possible  danger  to  navigation  that  may 
occur  on  any  ship  equipped  with  an  electric  plant. 

3.  The  Bureau  requests  that  copies  of  the  letter  may  be  printed  as  a  De- 
partment special  circular  and  issued  for  the  information  of  the  officers  of 
the  service  as  a  precautionary  measure  against  a  possible  and  unexpected 
danger  to  the  safe  navigation  of  a  ship,  the  only  remedy  for  which  lies  in 
increased  vigilance  when  the  electric  circuits  are  in  operation. 

Very  respectfully,  R.  B.  Bradford,  Chief  of  Bureau. 

The  Secretary  of  the  Navy. 


UNITED  STATES  STEAMSHIP  OREGON, 

Off  Woosung,  China,  May  1.  1901. 
Sir:     I    have    the    honor    to    submit    the    following    report    concerning 
the  effect   on   the   standard   compass   of   a   "ground"   in   the   bridge  electric 
circuit : 

2.  Just  before  sunset,  5:20  P.  jr.  April  16,  while  steaming  up  the  China 
coast  on  course  NE.  by  N.,  it  suddenly  became  necessary  to  change  the 
course  about  a  point  to  the  eastward  by  bridge  and  steering  compasses  to 
make  the  allotted  course  by  standard.  An  investigation  mado  it  appear 
that  the  trouble  was  with  the  standard  conipass.  A  Time  Azimutli  taken 
at  once  showed  this  to  be  the  ease,  as  the  deviation  of  standard  compass 
was  10  degrees  04  minutes  E.,  the  tal)ulated  deviation  being  1  degi'ee  04 
minutes  E. 

3.  Tlic  tioublc  was  at  once  attril)ulc(l  (o  a  ••ground"  in  llic  clcclric  cir- 
cuit, and  upon  inquiry  it  was  found  that  tlie  bridge  circuit  liad  just  been 
turned  on.  This  was  turned  off  at  once,  when  the  standard  compass  re- 
sumed its  normal  condition,  a  second  Time  Azimuth  sluiwing  a  deviation  of 
1  degree  09  minutes  E. 

4.  The  bridge  circuit  was  onh'rcd  luiiicd  on  again  for  experiment,  when 
the   cou'pass-card    of    standard    was    dliseivcd    to    ukivc    rapidly    Ihrougli    an 


Dkviatiox.  209 


arc  of  alxmt   10  degrees.     The  circuit   was  again  turned  nlV  and  oil-lanijis 
were  used  tliroughout  the  night. 

5.  A  search  for  the  "ground"  was  begun  tlie  next  day  and  it  was  finally 
located  in  the  starboard  after  searcli-light  control,  '{"his  being  cut  out,  tlie 
remainder  of  tlie  bridge  circuit  was  turiied  on  wilhonl  exerting  any  inllu- 
enee  on  the  compass. 

6.  The  standard  compass  is  mounted  on  a  raised  platform  on  the  after 
part  of  the  bridge  deck.  Tliis  platform  is  4  feet  2  inches  wide  and  8  feet  8 
inches  long.  It  stands  about  9  feet  above  the  bridge  deck;  is  mounted  on 
four  brass  stanchions,  and  has  a  perpendicular  brass  ladder  at  the  after 
side.  A  brass  hand-rail  runs  around  the  platform,  the  upper  rail  being 
about  the  height  of  the  compass-card.  This  rail  passes  2  feet  from  the  cen- 
ter of  tlie  compass-card  on  the  starboard  and  port  sides,  and  2  feet  9  inches 
from  the  center  of  the  compass-card  on  the  forward  side.  The  search-light 
control  is  3  feet  below  the  after  end  of  the  bridge  deck,  making  it  17  feet 
below  and  17  feet  abaft  the  compass-card  of  standard,  and  about  1  foot  to 
starboard  of  amidship  line.  The  nearest  wires  to  the  compass  pass  on  the 
underside  of  the  bridge  deck  in  the  midship  line,  14  feet  below  the  compass. 

Very  respectfully,  F.  M.  Bostwick, 

Lieutenant  Coiniuinidcr  V.  8.  A^,  Navif/ator. 
The  Commanding  Officer. 

A  good  result  will  always  be  had.  providing  the  sun  or  star  has 
not  an  altitude  greater  than  40°.  This  will  be  easily  understood, 
for  the  reason  that  the  greater  the  altitude,  the  more  difficult  it 
will  be  to  get  a  good  observed  bearing ;  theoretically  speaking,  it  is 
always  possible  to  determine  the  deviation  at  any  time  when  the  sun 
or  a  star  is  visible,  but  it  is  not  possible  from  a  practical  point  of 
view,  as  before  remarked. 

It  should  always  be  borne  in  mind  by  the  navigator  that  the  de- 
viation found  is  only  for  the  direction  of  the  ship's  head  at  the 
time  of  taking  the  bearing,  and  only  for  that  particular  part  of  the 
world  where  the  observer  happened  to  be  at  the  time,  and  for  no 
other.  The  ship  should  also  be  steadied  on  a  course  at  least  seven 
minutes  before  a  bearing  is  taken,  to  overcome  as  nnu'h  as  possible 
the  retentive  magnetism,  whieh  is  always  a  doulitful  quantity. 
amounting  to  as  much  as  one  and  a  half  points  under  certain  con- 
ditions, and  this  assertion  is  made  from  the  personal  experience- 
of  the  author. 

When  swinging  a  ship  to  find  tlie  deviation  alone,  at  least  two 
hours  should  be  taken,  and  the  writer  here  wishes  to  caution  the 
student  in  regard  to  a  tendency  among  a  certain  class  of  seamen 
to  perform  hurry-u]i  jobs  and  to  In-ag  afterwards  how  short  a 
time  they  could  do  it  in.  I  have  frequently  heard  old  navigators 
bragging,  and  recall  one  particular  case — that  of  a  master  of  a  large 

Taylor's   Mod.   Nav.   14. 


210  T.vYLOii'y   MoDEitx    Xavigatiox. 

passenger-steamer,  who  simply  slowed  the  engines,  then  put  the 
helm  hard  over,  and  took  the  hearings  as  the  ship  flew  around, 
without  once  steadying  the  helm.  When  asked  how  the  result 
came  out  in  such  cases,  he  said,  "Well,  it  may  not  be  quite  correct ; 
but,  then,  I  always  have  a  good  lookout  kept."  And  he  is  only  one 
of  many  others  where  a  good  lookout  is  the  only  thing  that  keeps 
them  off  the  rocks. 

On  board  vessels  plying  on  the  United  States  coasts,  it  is  a  very 
rare  occurrence  to  swing  a  ship  and  take  azimuths;  the  master 
simply  notes  the  course  between  points  on  a  clear  day,  and  if  she 
"fetches"  a  little  inshore,  he  keeps  her  out  a  little  next  trip,  or  the 
contrary,  and  if  asked  any  questions  in  regard  to  the  amount  of 
deviation  on  his  navigating-compass,  he  cannot  give  the  slightest 
information  about  it. 

As  a  case  in  point,  the  following  incident  came  under  the  writ- 
er's notice:  Some  years  ago  a  certain  vessel  touched  bottom,  but 
managed  to  reach  port.  At  the  inquiry  the  master  was  asked  to 
produce  a  deviation-card.  He  informed  his  inquisitors  that  he  did 
not  have  it  with  him;  so  he  was  ordered  to  produce  it  next  day.  In 
the  interval,  not  having  a  card,  he  enlisted  the  services  of  a  friend 
to  help  him  make  one  to  fit  the  courses  given  in  his  testimony.  It 
was  done,  and  the  master  was  exonerated.  This  is  a  very  bad  case, 
but  it  will  go  to  show  the  criminal  carelessness  and  ignorance  of 
some  coasting-navigators,  if  you  can  call  them  such;  but  we  are 
very  glad  to  state  that  the  above  is  an  extremely  rare  case. 

The  excuse  most  masters  give  for  not  swinging  ship  is  that  the 
owners  will  not  give  them  time ;  but  this  is  a  very  lame  excuse,  for 
no  owner  with  any  business  sense  will  prevent  the  master  from 
doing  what  he  considers  necessary  for  the  safety  of  the  vessel ;  and 
supposing  the  owner  does  object  to  the  delay  and  expense,  the 
master  has  plenty  of  time  when  the  owner  cannot  see  him,  provid- 
ed he  knows  how;  and  it  is  the  province  of  this  book  to  tell  him.  if 
ho  is  not  already  in  possession  of  the  requisite  knowledge. 

Should  the  master  not  be  able  to  take  azimuths,  there  are  several 
other  methods  of  determining  tbe  deviation.  The  first  is  by  using 
Napier's  Diagram,  as  already  described,  and  l)y 

I\((>tg('-I)<'ariiigs. 

There  are  minu'rous  ranges  on  our  coasts  and  in  our  luirbors,  if 
the  navigator  will  only  use  them.  The  United  States  government 
prints  and  j)ublishes  charts  of  ranges  for  tlu'  benefit   of  seamen. 


Dkviatiox.  211 


which  may  1)0  procured  from  the  local  Hydrograjjlnc  officials  by 
simply  asking  for  them.  These  ranges  may  be  utilized  after  the 
following  manner : 

Place  the  ship's  head  on  a  certain  course  upon  which  the  devia- 
tion is  desired ;  bring  ship  in  line  with  the  range  and  take  a  bearing 
by  the  compass,  and  the  difference  between  the  compass  bearing 
and  the  magnetic  bearing  taken  from  the  chart  will  be  the  devia- 
tion, to  be  named  East  if  the  magnetic  bearing  is  to  the  right  of 
the  compass  bearing,  and  ^Yest  if  to  the  left. 

Some  of  the  published  ranges  are  of  very  little  practical  value, 
because  they  are  at  right  angles,  or  nearly  so,  to  the  set  of  the  tides ; 
therefore  only  those  ranges  running  in  the  same  or  in  the  opposite 
direction  to  the  set  of  the  tides  should  be  used,  so  that  the  vessel 
can  be  steadied  on  the  course  a  sufficient  length  of  time.  If  the 
range  runs  athwart  the  tide,  the  ship  is  swept  out  of  range  so 
quickly  that  it  is  hard  either  to  get  a  good  bearing  or  to  steady  her 
head. 

There  is  yet  another  good  way  of  getting  the  deviation,  but  it 
has  one  bad  point,  and  that  is,  it  requires  two  men  to  do  it — one 
on  shore  and  the  other  on  board — and  the  element  of  doubt  is, 
whether  the  man  on  shore  is  attending  to  business. 

This  method  is  called  Reciprocal  Bearings,  and  is  popular  in 
European  countries,  but  is  not  much  used  in  America.  It  is 
carried  out  after  the  following  manner : 

Place  a  compass  on  shore  in  such  a  position  that  it  will  not  be 
affected  by  iron;  in  other  words,  so  that  it  will  show  magnetic  and 
be  visible  from  the  ship.  The  man  on  shore  must  be  instructed  to 
take  a  bearing  of  the  ship  when  a  prearranged  signal  is  made,  and 
to  number  the  bearings.  The  man  on  board  must  always  keep 
within  sight  of  the  man  on  shore,  and  after  steadying  the  ship's 
head  on  a  certain  course  he  must  make  a  signal  and  take  a  bearing 
of  the  man  on  shore,  and  the  man  on  shore  must  take  a  bearing  of 
the  ship.  When  a  sufficient  number  of  bearings  have  been  taken 
and  the  shore  observer  is  brought  on  board,  all  the  shore-bearings 
must  be  reversed.  As  they  wall  be  magnetic,  the  difference  be- 
tween the  reversed  shore-bearings  and  the  bearings  from  the  ship 
will  be  the  deviation,  to  be  named  as  before  explained.  As  a  final 
word  of  caution,  l)c  it  remembered  that  the  results  iti  all  the  dif- 
ferent methods  will  dei)end  upon  the  care  exercised  by  the  observer. 


213  Taylor's  Modern  Navigation. 

and  he  must  not  at  any  time  be  careless,  as  on  the  care  exercised  the 
safety  of  the  ship  will  depend. 

INSTEUMENTS  USED  ON  BOARD  SHIPS  FOR  TAKING 
BEARINGS. 

There  are  numerous  instruments  in  use  for  this  purpose.  Some 
of  them  are  called  compass-correctors,  which  is  a  misnomer.  They 
should  be  named  deviation-detectors.  Others  are  so-called  labor- 
saving  devices,  their  greatest  value  consisting  in  the  fact,  from  the 
inventor's  point  of  view,  that  no  azimuth  tables  are  required;  but 
in  the  author's  opinion  these  devices  are  simply  toys,  correct  in 
theory,  but  in  actual  practice  not  to  be  relied  upon,  owing  to  the  in- 
tricate nature  of  their  construction  and  liability  to  get  out  of  order 
by  rough  usage. 

This  matter  of  entirely  dispensing  with  azimuth  tables  is  wrong, 
and  no  owner  or  shipmaster  should  waste  money  on  useless  instru- 
ments for  a  more  accurate  result  will  be  had  by  using  the  tables 
than  by  the  use  of  these  catchpenny  instruments,  the  principal 
claim  of  the  so-called  inventors  being  that  the  tables  are  entirely 
unnecessary. 

Azimuth  tables  are  the  most  useful  publications  issued  by  the 
United  States  government,  for  not  only  can  the  deviation  be  found 
with  great  accuracy  and  few  figures,  but,  as  already  explained  in  the 
modern  method  of  determining  ship's  position,  they  are  absolutely 
necessary  in  the  modern  practice  of  navigation.  If  it  were  not  so, 
the  United  States  Hydrographic  Otfice  would  not  bother  about 
printing  and  selling  them  for  so  ridiculously  small  a  sum  as  that 
for  which  they  are  sold  to  the  navigator. 

Wc  speak  in  the  above  forcible  manner  because  navigators  are 
likely  to  be  misled  l)y  the  desire  of  storekeepers  to  sell  an  instru- 
ment of  which  they  have  not  the  slightest  knowledge;  their  only  ob- 
ject in  selling  being  the  liberal  commission  allowed  by  the  maker. 

The  most  serviceable  and  useful  instrument  is  called  the  Felorus, 
a  cut  of  which  is  printed  in  this  article.  It  is  simply  a  dumb-card 
whereon  is  engraved  the  points  and  degrees  of  the  compass,  balanced 
so  as  to  swing  free  in  the  gimbals.  It  is  an  instrument  to  measure 
the  angle  between  the  ship's  head  and  the  object  observed.  Sight- 
vanes  are  attached  to  enable  the  observer  to  get  a  line  of  sight.  A 
milled-head  clamp-screw  is  ])rovided,  situated  in  llu'  center,  to  clamp 
the  siffht-vanes  whenever  it  is  necessarv  to  do  so.       Another  small 


Deviation. 


213 


screw  will  be  found  on  the  outer  cdg-e  of  the  plate,  which  is  used 
to  clamp  the  inner  plate  to  the  ring. 

This  instrument  is  generally  of  such  solid  construction  that  if 
it  happened  to  take  a  journey  into  the  lee  scuppers  little  or  no 
damage  would  be  done  to  it,  except  that  the  sight-vanes  might  be 
bent,  but  this  would  be  easily  detected  and  as  easily  repaired, 
whereas  the  labor-saving  devices,  so  called,  if  they  went  on  the  same 
trip,  would  be  irretrievably  ruined. 

Before  using  the  Pelorus,  it  is  of  the  utmost  importance  that  it 
be  placed  correctly,  namely,  so  that  a  fore-and-aft  line,  or  a  line 
which  is  parallel  to  it,  will  pass  through  the  center  of  the  card  and 
the  lubber-point  on  the  outer  ring.  If  this  is  not  correctly  done, 
all  observations  taken  by  it  will  be  in  error;  therefore  great  care 
should  be  taken,  and  if  the  navigator  has  not  the  requisite  knowl- 
edge, some  experienced  person  should  be  employed. 

In  regard  to  the  placing  of  the  Pelorus  it  is  not  always  advisable 
to  enlist  the  services  of  an  employee  of  a  ship-yard,  for  the  writer 
has  seen,  many  times,  such  men  finding  the  line  by  the  seams  on 
the  deck  or  by  measuring  simply  from  the  side  of  a  house  and 
taking  the  middle  of  the  house  for  a  center  line.  It  is  hardly  neces- 
sary to  state  that  such  work  is  liable  to  be  in  error.  The  proper 
way  is  to  work  from  stem  of  ship  to  stern-post,  and  if  there  are  any 
obstructions  in  line  of  sight,  measure  to  one  side  or  the  other  a 
certain  number  of  feet  until  a  clear  view  can  he  had  fore  and  aft, 
and  refer  this  line  to  the  center,  or  to  any  place  where  it  is  re- 
quired to  place  the  Pelorus-stands.     There'  should  be  at  least  two 


214  Taylor's  Moderx  ?s' avigatiox. 

of  these  stands,  one  on  each  side  of  the  bridge,  so  that  if  the  smoke- 
stack, sails,  or  a  boat  obstructs  the  line  of  sight,  the  Pelorus  may 
be  shipped  on  the  other  side. 

The  Pelorus  being  accurately  placed  in  its  proper  stand,  we  will 
now  explain  the  different  methods  of  using  it. 

First  Method. — To  find  the  observed  bearing  of  a  distant  object, 
either  of  the  sun,  a  star,  or  land. 

Place  the  same  course  that  you  are  steering  on  the  lubber-point  of 
the  Pelorus ;  keep  the  vessel  steady  on  her  course ;  move  the  sight- 
vanes  until  the  object  is  seen  directly  through  them,  and  cut  by  the 
thread,  then  clamp  them;  read  what  is  on  the  Pelorus,  and  this 
reading  will  give  the  observed  bearing  of  the  object.  If  taking  an 
azimuth  amplitude  or  bearing  of  the  land,  this  would  be  the  com- 
pass-bearing. 

Second  Method. — To  set  the  ship's  head  correct  magnetic. 

Enter  the  time  azimuth  tables  and  take  therefrom  the  sun's  true 
azimuth  corresponding  to  the  apparent  time  at  ship,  the  latitude, 
and  declination,  being  careful  to  note  if  the  latitude  and  declination 
are  of  same  name  or  of  contrary  names ;  to  this  true  bearing  taken 
from  the  azimuth  tables  apply  the  variation  of  the  place,  allowing 
easterly  to  the  left  and  westerly  to  the  right;  the  result  will  be  the 
magnetic  azimuth;  place  the  sight-vanes  to  this  magnetic  azimuth 
and  clamp  them;  place  the  magnetic  course  that  you  wish  to  steer 
on  the  lubber-point  and  clamp  it  also,  then  port  or  starboard  the 
helm  until  the  object  is  seen  directly  through  the  sight-vanes ;  the 
ship  will  then  be  on  the  magnetic  course,  which  is  clamped  on  the 
lubber-point.  If  the  deviation  is  required,  it  will  l)e  found  in  this 
manner. 

The  course  set  on  the  Pelorus  is  the  correct  magnetic  course,  and 
the  difference  between  it  and  the  one  shown  by  the  compass  will  be 
the  deviation  for  whatever  the  ship  was  heading  at  the  time,  to  be 
named  easterly  if  the  correct  magnetic  course  is  to  the  right,  and 
westerly  if  to  the  left  of  the  compass  course. 

Third  7l/e^//.0f/.— Slacken  all  the  screws  in  the  Pelorus,  clamp  the 
sight-vanes  to  the  magnetic  bearing  of  the  sun,  keeping  the  ship 
steady  on  her  course ;  move  the  sight-vanes,  which  are  clamped  to 
the  plate,  until  the  object  is  seen  through  them ;  when  this  is  done 
nicely  and  the  ship  is  still  steady  on  her  course,  clamp  the  plate; 
the  course  indicated  on  tlu'  liil)bcr-poiiit  of  the  PcU)rus  will  be  the 


Deviation.  215 


correct  magnetic  course  the  ship  is  steering  at  the  time,  and  the 
difference  between  this  magnetic  course  and  the  one  shown  by  the 
compass  will  be  the  deviation,  to  be  named  easterly  if  the  Pelorus 
is  to  the  right  of  the  compass  course  and  westerly  if  to  the  left. 

KuLE  TO   Use   Field's   Pelorus. 

It  will  be  noticed,  when  using  this  Pelorus,  that  there  are  two 
circles,  the  outer  one  being  given  in  degrees,  starting  from  0°  and 
reaching  to  180°,  and  the  inner  one  being  a  representation  of  a 
compass,  but  with  the  East  point  placed  where  the  West  ought  to  be. 
This  method  of  turning  the  compass  around  is  a  very  handy  one 
when  it  is  understood.  For  instance,  place  the  box  on  the  correct 
fore-and-aft  line,  or  a  line  which  is  parallel  to  it,  the  same  as  in 
the  previous  methods;  bring  0°  of  the  outer  circle  so  that  it  will 
come  in  a  direct  line  with  ship's  head;  then  bring  South  of  the 
inner  plate  so  that  it  will  be  in  a  direct  line  also ;  move  the  South 
point  of  the  inner  plate  to  the  right  or  left,  according  to  the  name 
and  amount  of  the  variation;  then  clamp  the  inner  and  outer 
plates  together.  (The  above  method  is  to  be  used  for  north  lat- 
itude only,  but  if  in  South  latitude,  simply  bring  the  North  to  the 
0°  instead  of  the  South.) 

Now  enter  the  azimuth  tables  and  take  therefrom  the  true  bear- 
ings; watch  where  the  shadow  of  the  center-pin  falls,  and  on  the 
inner  plate  will  be  indicated  the  magnetic  course  the  ship  is  steer- 
ing; the  difference  between  this  and  what  the  ship  is  heading  at  the 
time  will  be  the  deviation,  to  be  named  the  same  as  in  the  preced- 
ing rule.  If  the  shadow  of  the  pin  does  not  fall  on  the  course  that 
you  wish  to  make,  then  port  or  starboard  the  helm  until  it  does; 
the  ship  will  then  be  steering  the  correct  course  that  you  wish  to 
make. 

THE  SHADOW-PIN. 

Some  compasses  have  attachments  fitted  to  the  compass-bowl 
whereby  the  observed  azimuth  may  be  read  directly  from  the  card. 
This  is  the  best  and  most  reliable  way  ;  for  by  it  any  error  that  might 
occur  in  the  incorrect  placing  of  the  Pelorus  or  in  the  waj-ping  of 
the  stand  by  excessive  heat  would  be  entirely  eliminated. 

The  commonest  and  most  easily  understood  method  is  that  of 
the  shadow-pin,  but  it  has  several  drawbacks,  as  will  be  seen. 

The  pin  must  be  accurately  centered  in  the  bowl  that  is  at  a  point 


216  Taylor's  Modeen  Navigation. 

indicated  by  the  intersection  of  two  diameters,  and  must  be  at  right 
angles  to  the  plane  of  the  compass-card. 

The  pin  must  always  be  straight ;  if  not,  an  incorrect  reading  of 
the  card  will  be  taken.  To  test  the  pin,  proceed  in  the  following 
manner:  Place  it  in  position,  keep  ship's  head  steady,  and  note 
where  the  shadow  falls,  then  turn  the  pin  half  round  and  see  if  the 
shadow  falls  on  the  same  place.  If  so,  it  is  straight;  if  not,  it  is 
bent. 

The  pin  being  straight,  and  it  is  required  to  take  a  bearing  of  the 
sun,  note  where  the  shadow^  falls,  and  read  opposite;  but  it  will  be 
found  that  if  the  sun  has  a  very  low  altitude  there  will  be  no 
shadow  thrown  on  the  card,  and  if  it  has  a  high  altitude,  the  shadow 
will  not  reach  as  far  as  the  edge  of  the  card. 

Still,  with  these  drawbacks,  it  is  a  very  useful  thing  to  use,  pro- 
vided the  observer  is  careful  to  see  that  the  pin  is  straight. 

Last,  but  not  least  important,  is  Thompson's  Azimuth  Mirror, 
supplied  with  Thompson's  Compensating  Binnacle,  the  most  ac- 
curate instrument  for  determining  azimuths  in  existence,  and  so 
easy  to  handle  that  inside  of  five  minutes  from  the  time  of  first 
taking  hold  of  it  the  navigator  can  be  an  expert  observer.  Printed 
instructions  are  supplied  with  each,  so  that  it  is  unnecessary  to 
give  them  here. 

This  is  not  an  advertisement,  for  the  compass  and  mirror  do  not 
reed  my  indorsement,  as  they  are  now,  and  have  been  for  a  number 
of  years,  in  use  on  board  of  our  largest  steamers. 

There  are  several  other  instruments  in  use,  but  lack  of  space  com- 
pels us  to  mention  only  those  most  frequently  found  on  board  ships. 


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DIVISION  IX. 

CHART-WOEK. 

Before  proceeding  with  chart-work  itself,  we  will  endeavor  to 
give  a  description  of  the  instruments  used  for  this  class  of  work, 
and  also  a  description  of  the  different  kinds  of  charts. 

The  Parallel  Ruler. 

This  instrument,  if  such  a  name  may  properly  be  applied  to  it, 
consists  of  two  pieces  of  w^ell-seasoned  ebony  with  brass  joints,  and 
is  used  for  referring  a  line  to  one  of  the  compasses  printed  on  a 
chart  so  that  the  course  may  be  found,  or  when  taking  bearings  of 
the  land  to  refer  the  same  from  the  compass  to  the  point  observed. 
The  navigator  should  test  it  after  the  following  manner:  Exam- 
ine the  bearings  and  see  if  they  work  easily,  but  they  should  not 
be  too  slack,  for  if  they  are,  it  is  possible  for  the  edges  to  get  out 
of  parallel;  then  see  if  the  two  outer  edges  also  are  parallel;  this 
may  be  done  by  drawing  a  straight  line  on  a  piece  of  paper  with 
the  assistance  of  one  edge  of  the  rulers;  then  advance  the  rulers, 
say,  about  a  foot,  and  draw  another  line;  then  place  the  other  edge 
of  the  rulers  to  the  lower  line  and  advance  towards  the  upper  one 
again  and  see  if  the  second  edge  lies  exactly  along  it;  if  so,  the 
two  edges  are  parallel,  if  not,  reject  the  rulers.  It  should  be  borne 
in  mind  that  although  these  rulers  are  made  of  well-seasoned 
ebon}'-,  still  they  are  likely  to  warp  in  the  course  of  time,  there- 
fore the  navigator  ought  to  test  them  frequently,  or  he  is  lial)le  to 
lay  the  course  off  maybe  a  quarter  of  a  point  in  error. 

The  above  description  is  of  the  regular  ruler,  so  common  in 
every-day  use  that  mention  seems  unnecessary;  still,  the  writer  has 
seen  many  men  using  rulers  that  had  as  much  as  a  quarter  of  an 
inch  play. 

Field's  Parallel  Uider. 
This  is  an  instrument  that  makes  compasses  printed  on  a  chart 
unnecessary;  for  if  the  navigator  will  only  take  the  trouble  to  ex- 
amine one  of  these,  he  will  find  one  edge  of  it  graduated  to  degrees. 
Jt  will  also  be  noticed  that  on  chart?  of  large  localities,  like  ocean 
or  track  charts,  the  compasses  printed  on  them  are  at  widely  differ- 
ent places,  making  it  necessary  for  the  navigator  to  "scull''  from 
one  side  of  the  chart  to  the  oth^i',  l)er()rc  he  can  get  the  course; 
and  if  there  is  any  error  in  lh(^  parallelism  of  the  rnlcrs.  it  is  in- 
creased everv  time  he  moves  them:  and  if  there  is  no  error,  they 


CllAKT-WORK.  ^r.) 


iire  still  liahlc  In  slip,  if  he  is  not  vci'v  earcl'iil.  By  the  use  of 
Field's  ruler  it  would  l)e  luucli  easier  to  p't  tlu'  course,  for  liv 
simply  moving  the  rulers  until  the  mark  in  the  center  of  the  blank 
side  is  on  a  true  meridian,  then  bringing  both  parts  together,  and 
reading  the  degrees  on  the  other  edge  which  cut  with  the  same 
meridian,  the  true  course  will  be  found.  Some  of  these  rulers — 
the  very  latest — have  brass  arms  arranged  so  that  they  will  tum- 
ble over,  making  it  unnecessary  to  slide  them.  This  is  a  very  good 
plan,  for  by  the  use  of  these  rulers  the  chart  is  not  soiled,  as  it  is 
when  sliding  rulers  are  used. 

Tlic  Transparent  Protractor. 

The  handiest  of  all  instruments  is  the  Transparent  Protractor, 
as  will  be  seen. 

Bute — Place  the  hole  in  the  center  of  the  Protractor  over  the 
position  of  the  ship  on  the  chart;  then  set  the  edge  of  the  Pro- 
tractor true  by  the  parallel  lines  around  its  edge,  cutting  or  run- 
ning parallel  to  a  true  meridian  on  the  chart ;  then,  if  the  true 
course  is  required,  stretch  the  thread  to  any  point,  and  the  reading 
on  the  compass  where  the  thread  passes  over  will  be  the  true  course. 

If  the  compass  course  is  required.  With  the  thread  draw  a  true 
Xorth  line  and  keep  it  taut;  hold  the  Protractor  with  its  center 
ever  ship's  position,  with  the  other  hand  turn  the  Protractor  to  the 
East  or  to  the  West  the  amount  of  variation  and  deviation;  hold 
protractor  steady  and  shift  the  thread  to  the  place  you  wish  to 
steer  for.  and  where  it  cuts  the  compass  will  be  the  compass  course 
to  steer. 

THE  THREE-ARM   PROTRACTOR.  OR   STATIOX- 
POINTER. 

This  instrument,  until  very  recently,  was  very  little  known, 
and  at  the  present  time,  although  quite  a  number  talk  wisely  about 
it.  very  few  seamen  have  ever  seen  it,  unless  they  have  at  some  time 
paid  a  flying  visit  to  a  United  States  man-of-war  or  a  surveying- 
^■essel.  Thq  reason  of  this,  however,  is  its  cost,  as  owing  to  the 
limited  salary  enjoyed  ( ?)  by  licensed  officers,  they  cannot  be  ex- 
pected to  purchase  one  for  themselves;  but  as  one  instrument  is 
sufiieient  for  a  vessel,  I  think  that  the  owners  ought  to  supply  it, 
as  it  is  especially  to  their  interest  for  the  ship  to  make  as  quick  a 
passage  as  possible.  Tn  fact,  all  navigating  ap]ilianees  should  be 
supplied  to  ships  by  the  owners,  for  they  lose  many  a  dollar  by 


220  Taylor's  ]\Iodekx   Xavigatiox. 

the  master  and  officers  attemi^ting  to  navigate  the  vessel  with  obso- 
lete charts  and  worn-out,  old-fashioned  instruments. 

An  illustration  of  this  useful  instrument  ma}'  be  seen  in  the 
American  Bowditch  E23itome,  with  a  more  or  less  lucid  explanation; 
still,  there  may  be  some  that  cannot  understand  what  is  there  given, 
therefore  I  will  endeavor  to  explain  further  here. 

The  principle  upon  which  the  instrument  is  constructed  is  as 
follows : 

Through  any  three  points,  not  in  a  straight  line,  a  circle  can  be 
drawn.  Try  it  thus:  Make  three  marks,  not  in  a  straight  line, 
within  the  scope  of  the  dividers. 

Take  anything  more  than  one  half  the  distance  between  two  of 
the  marks,  and  with  one  foot  of  the  dividers  on  one  of  them  de- 
scribe a  circle;  with  the  same  space  in  dividers  place  one  leg  on 
the  other  mark  and  draw  another  circle;  then  through  the  two 
points  of  intersection  of  the  circles  draw  a  line  of  indefinite  length ; 
then  do  the  same  with  the  other  marks  and  draw  another  line,  and 
at  the  point  where  this  last  line  cuts  the  first,  place  a  leg  of  the 
dividers  and  measure  out  to  either  of  the  three  marks  and  describe 
a  circle.  It  will  then  be  seen  that  the  circle  passes  through  all  of 
them.  For  further  instruction  in  regard  to  the  above,  the  student 
is  referred  to  any  good  book  on  elementary  geometry. 

The  usefulness  of  this  instrument,  we  hope,  will  be  thoroughly 
appreciated  by  the  simple  fact  that  bearings  of  tlie  land  l)y  com- 
pass are  unnecessary.  This  is  a  very  great  recommendation,  when 
we  take  into  consideration  how  doubtful  the  compass  errors  are, 
owing  to  the  extensive  use  of  iron  nowadays. 

It  should  be  borne  in  mind,  however,  that  a  correct  result  de- 
pends very  much  on  the  accuracy  of  the  chart  and  on  the  fact  that 
three  distant  objects  must  be  visible  at  same  time. 

To  Observe. 

Station  two  officers  with  tlu'ir  st'xtaiits.  one  to  iiu'a>inv  from 
the  center  object  to  the  right  and  the  other  to  measure  to  the  left; 
these  two  angles  must  then  be  set  on  the  instrument ;  the  one  to 
the  right  must  be  clamped  to  the  right  of  tlie  fixed  arm  in  center, 
and  the  other  must  be  clamped  to  the  left  of  it ;  then  when  all 
three  arms  are  fixed  lay  the  Protractor  on  the  chart  so  tliat  the 
three  arms  will  point  to  each  of  the  three  objects  observed  ;  when 
this  is  done,  make  a  mark  on  the  chart  directly  under  tlie  center 


CiiAin-WuKK.  221 


of  tho  circle.  This  will  be  ship's  position.  With  the  assistance 
of  a  piece  of  tracing-paper,  as  describetl  in  liowilitcli.  tlio  operation 
is  still  more  graphic. 

There  may  be  some  awkwardness  at  first  when  mcasiiring  hori- 
zontal angles,  but  practice  will  make  perfect;  and  if  the  master 
of  a  ship  will  only  insist  that  his  oflficers  shall  be  experts  in  such 
matters,  they  will  undoubtedly  learn. 

DIVIDERS. 

This  simple  little  instrument,  which  is  so  very  necessary  in 
navigation,  needs  no  description  here,  yet  care  should  be  taken  in 
its  selection. 

Dividers  should  work  smoothly  on  the  joints,  but  should  not 
be  slack.  Keep  them  so  that  when  opened  a  certain  space  they  will 
retain  their  position.  The  best  makes  have  an  appliance  so  that 
they  may  be  tightened  with  a  key.  This  is  much  better  than  con- 
tinually clinching  them  witli  a  hammer,  as  must  he.  done  with  the 
cheap  variety. 

The  points  should  be  even  and  well  tempered,  so  that  they  will 
not  bend.  It  is  not  desirable  that  they  should  be  very  sharp,  as 
they  are  likely  to  penetrate  the  chart  if  the  navigator  has  a  heavy 
hand. 

CHARTS. 

We  have  in  the  United  States  three  ditferent  kinds  of  charts. 
They  are  called : 

1.  The  Gnomonic  Projection,  which  is  used  exclusively  for  deter- 
mining the  Great  Circle  Track. 

2.  The  Polyconic  Projection,  until  very  recently  was  the  method 
used  for  United  States  coasting-charts,  but  at  the  present  time  is 
used  only  for  charts  of  large  localities  and  for  harbor-charts. 

3.  Mercator's  Projection,  wliich  is  the  method  used  at  the  pres- 
ent time  to  chart  our  coasts,  is  much  more  convenient  than  the 
Polyconic.  It  is  also  the  method  used  in  Great  Britain.  This 
fact  is  important,  because  when  an  American  chart  cannot  be  pro- 
cured, the  navigator  may  be  able  to  obtain  a  l^ritish  one. 

To  distinguish  one  projection  from  another,  read  tlie  following: 
Place  the  chart  so  that  you  look  Xorth  ;  tlien  notice  if  the  merid- 
ians are  always  the  same  distance  apart,  and  also  if  the  parallels 


222  Taylor's  ]\Iodekx  Xavigatiox. 

running  to  the  East  and  West  are  at  right  angles  to  them;  if  so. 
then  it  is  a  Mercator's  chart;  but  if  the  meridians  converge  as  you 
go  towards  the  pole,  either  North  or  South,  then  it  is  a  Polyconie 
chart.  If  the  navigator  is  still  in  doubt,  ho  will  find  the  neces- 
sary information  printed  among  the  remarks. 

It  is  very  important  that  this  should  be  understood  before  using 
a  chart,  on  account  of  the  necessity  of  plotting  the  ship's  position 
and  of  measuring  the  distance,  which  is  different  on  a  Mercator 
from  what  it  is  on  a  Polyconie  chart.  The  method  of  doing  so 
will  be  explained  further  on. 

To  know  if  the  chart  is  for  Xorth  or  South  latitude,  and  for 
either  East  or  West  longitude,  read  the  following: 

Face  the  North  as  before,  and  see  if  the  degrees  of  latitude  in- 
crease or  decrease  towards  the  North  or  South.  If  they  increase 
towards  the  North,  it  is  a  North-latitude  chart,  Imt  if  they  de- 
crease, it  is  a  South-latitude  chart. 

If  the  degrees  of  longitude  increase  towards  the  West,  it  is  a 
West-longitude  chart,  but  if  they  increase  towards  the  East,  it  is 
an  East-longitude  chart. 

To  know  if  it  is  a  true  or  magnetic  chart,  read  the  following; 

In  regard  to  this  subject  it  will  be  found,  by  inspecting  a  few 
United  States  coasting-charts,  that  both  the  true  and  magnetic 
compasses  are  given  on  some  of  them,  while  on  the  others  either 
true  or  magnetic  only  is  given,  and  if  the  words  "True  Compass" 
or  "Magnetic  Compass"  are  not  printed  on  the  chart,  which  chart 
it  is  may  be  found  after  the  following  manner : 

Place  the  North  part  of  chart  in  front  of  you  and  examine  the 
compasses  thereon,  and  if  the  North  and  South  are  printed  right 
on  or  parallel  to  a  true  meridian,  then  it  is  a  true  chart,  but  if  they 
are  slewed  out  of  the  Meridian,  either  one  way  or  the  other,  then  it 
is  a  magnetic  chart. 

Most  coast  charts  are  magnetic,  while  oci'an  track  eliavts  are 
true;  tlierofore.  wlicn  using  tlie  true  chart,  both  variation  and  de- 
viation, if  any,  must  be  used  to  obtain  a  compass  course  to  steer; 
but  when  a  magnetic  chart  is  used,  deviation  only  is  to  be  applied 
to  obtain  a  compass  course,  allowing  East  to  tlio  left  and  West  to 
the  right,  which  is  the  opposite  rule  to  that  used  in  the  day's  work. 

Variatio7i.— On  the  United  States  coasting-charts,  the  amount  of 
variation  for  the  localities  is  printed  on  the  chart,  in  or  near  the 
compasses,  with  the  amonnt   o\'  animal   cliange.  aiul   in   regard  to 


(iiAiri-WoKK.  253 


this  change  the  navigator  cannot  be  too  careful,  for  in  some  parts 
of  the  world  it  is  considerable,  whereas  in  others  it  is  so  small  that 
in  a  man's  lifetime  it  will  not  change  to  any  practical  amount.  If 
the  change  is  considerable,  the  navigator  should  examine  the  date 
of  publication,  and  if  it  is  an  old  chart,  and  a  later  one  cannot  be 
procured,  he  should  allow  for  the  change,  being  careful  to  note  if 
it  is  increasing  or  decreasing.  But  charts  are  published  by  the 
United  States  government  at  so  small  a  cost  to  the  navigator  that 
any  one  too  mean  to  provide  himself  with  the  latest  edition  is  not 
fir  to  have  charge  of  a  ship;  and  here  again  we  wish  to  whisper  in 
tlie  ear  of  the  owner,  that  many  men  are  trying  to  navigate  ships 
with  obsolete  charts,  who,  with  a  knowledge  of  the  worthlessness 
of  these  charts,  arc  so  careful,  that  long  passages  are  the  result. 
Ship-owners  should  be  compelled  to  supply  to  ship-masters  all  the 
charts  that  may  be  required.  The  ship  would  then  be  navigated 
with  greater  safety,  and  quicker  passages  would  be  made. 

Ocean  track  charts  have  wavy  lines  running  across  them,  called 
lines  of  ecpial  variation;  therefore,  to  get  the  proper  variation  from 
such  a  chart,  the  navigator  must  select  that  line  which  is  closest 
to  the  ship's  position  and  search  along  it  until  the  amount  of  varia- 
tion is  found.  But  the  United  States  government  pul)lishes,  every 
year,  what  is  called  a  Variation  and  Dip  Chart,  whereby  the  varia- 
tion may  be  found  with  considerable  accuracy  by  simply  plotting 
the  ship's  position  on  same  and  taking  the  line  of  equal  variation 
closest  to  the  position.  All  ocean-going  vessels  should  have  a  copy 
on  board,  for  they  are  cheap  enough,  costing  only  about  fifty  cents. 
The  figures  on  charts  represent  the  depth  of  water  either  in  fath- 
oms or  in  feet  at  the  mean  of  lower  low  water.  Reference  should 
be  made  to  the  printed  instructions  to  determine  the  matter  of 
fathoms  or  feet.  The  letters  printed  close  to  the  figures  represent 
the  nature  of  the  bottom,  and  may  be  interpreted  by  referring  to 
the  table  of  signs  and  abbreviations  printed  for  the  purpose  among 
the  remarks. 

Scale  of  Charts. — A  large  scale  is  used  for  charts  of  small  locali- 
ties, such  as  harbor  charts;  but  charts  of  large  localities,  such  as 
ocean  charts,  are  necessarily  on  a  small  scale. 

PILOT-CHARTS. 

These  exceedingly  useful  charts  on  j\[ercat()i''s  projection  may  be 
procured  free  of  cost  from  the  local  ITydrographic  Office.  They 
are  not  intended  for  navigational  purpn-es.  in  tlie  strict  sense  of 


224  Taylor's  Moderx  Navigation. 


the  word,  JDut  to  assist  the  navigator  by  means  of  the  valuable  infor- 
mation contained  thereon,  and  are  to  be  used  in  conjunction  with 
other  charts  and  instruments,  such  as  barometers  and  thermome- 
ters. On  them  will  also  be  found  the  principal  Great  Circle  Tracks, 
with  lines  of  equal  variation.  These  charts  are  issued  monthly, 
and  the  real  object  of  their  publication  is  to  provide  the  navigator 
with  information  in  advance,  regarding  the  weather  to  be  expected 
and  the  probable  direction  of  the  wind,  the  latter  being  illustrated 
by  an  ingenious  system  of  symbols,  which  is  fully  explained. 

Valuahle  information  in  regard  to  currents  is  given,  with  their 
probable  direction  and  rate,  with  explanations  as  to  whether  per- 
manent or  surface,  or  if  influenced  by  winds  during  certain  sea- 
sons. The  position  of  derelicts  and  drifting  logs  is  stated,  with 
their  probable  position  calculated  for  the  future, — a  very  valuable 
bit  of  information  for  navigators,  putting  them  on  guard  so  that 
a  good  lookout  may  be  kept. 

Tracks  of  Circular  Storms  are  charted,  with  information  re- 
lating to  the  probable  place  of  formation,  curvature,  and  break-up, 
and  seasons  when  most  prevalent,  with  rules  for  handling  the  ship. 

A  sub-chart  of  Isobars  and  Isotherms  is  given,  cautioning  the 
navigator  in  regard  to  the  behavior  of  the  barometer  and  ther- 
mometer. 

Much  other  information  is  contained  on  the  charts,  extremely 
valuable  to  the  modern  navigator. 

As  a  final  word,  we  wish  to  direct  the  attention  of  the  navigator 
to  the  fact  that  most  of  the  information  contained  on  <:he  charts 
is  compiled  from  data  collected  by  the  Hydrographic  Office  from 
ship-masters  and  officers;  therefore,  whenever  it  is  possible,  records 
should  be  made  in  a  systematic  manner  of  all  changes  in  weather, 
passing  of  derelicts,  and  especially  of  the  behavior  of  the  barometer 
and  the  direction  and  force  of  tlie  wind  whenever  a  cireuUir  storm 
IS  encountered.  This  information  should  be  forwardrd  to  the 
Office  immediately  upon  ship's  arrival,  which  will  be  courteously 
acknowledged  by  the  officer  in  charge. 

The  master  should  insist  upon  liis  ollicers  ket'ping  the  meteorolo- 
gical log  on  the  blanks  furnished  for  the  ])ur])ose,  for  l)y  so  doing 
they  are  assisting  one  another  to  navigat<'  their  vesst'ls  with  a 
greater  degree  of  safety. 


CIIART-WOUK.  225 


To  Find  the  Course  between  Two  Places  on  a  Chart. 

Lay  tlu'  flat  edge  of  the  parallel  rulers  over  the  two  places  and 
move  theni  until  the  flat  edge  is  exactly  over  the  center  of  the  com- 
pass, then  read  the  course  from  the  side  of  the  printed  compass 
that  is  towards  the  place  it  is  desired  to  go  to;  this  will  be  the  true 
course  if  a  true  chart  is  used,  but  the  magnetic  course  if  a  magnetic 
chart  is  used. 

To  Find  the  Cotnijuss  Course  to  Steer  to  Make  Good  the  Course 
Taken  from  the  Chart. 

If  the  true  course  was  found,  apply  to  it  the  variation  for  the 
locality  the  ship  is  in,  allowing  East  to  the  left  and  West  to  the 
right :  the  result  will  be  the  magnetic  course. 

To  the  magnetic  course  apply  the  deviation,  allowing  East  to  the 
left  and  West  to  the  right;  the  result  will  be  the  compass  course 
to  steer. 

If  a  magnetic  chart  is  used,  no  attention  need  be  paid  to  the 
variation  further  than  what  has  been  previously  mentioned  in  re- 
gard to  date  of  chart;  the  only  correction,  therefore,  in  this  case 
i?  the  deviation,  to  be  applied  as  before  stated. 

The  above  rules  will  be  the  same  for  both  Mercator  and  Poly- 
conic  charts. 

To  Find  the  Distance  on  a  Mercator's  Chart. 

Take  the  space  between  the  two  places  in  the  dividers,  and  lay 
the  dividers  on  the  middle  latitude  abreast;  the  number  of  miles 
contained  between  them  will  be  the  distance,  provided  the  scope 
of  the  dividers  enables  the  taking  of  the  whole  distance  at  once; 
if  not,  take  one  half  or  one  third  of  the  space,  proceed  as  before, 
and  multiply  accordingly. 

To  find  the  distance  on  a  Polyconic  chart  reference  must  be 
made  to  the  scale  of  nautical  miles  provided  for  the  purpose,  and 
the  distance  must  not.  under  any  eii'eiiiustances'.  be  measured  on 
the  latitude  side  oF  the  chart. 

To  Plot  Latitude  and  Longitude  on  a  Mercator  Chart. 

Select  from  the  latitude  side  of  chart  the  number  of  degrees,  and 
with  the  dividers  measure  the  required  number  of  minutes;  with 
this  space  in  dividers,  move  across  the  chart  abreast  of  the  proper 
degree  until  the  nearest  degree  of  longitude  is  found,  and  on  the 

Taylor's   Mod.   Nav.   15. 


Taylou's  Modern  Xavioatiox. 


meridian  measure  the  odd  minutes  and  make  a  distinct  mark;  now 
lay  the  rulers  exactly  along  a  parallel  and  move  them  until  the  flat 
edge  is  over  this  mark  and  draw  a  line ;  the  ship  will  be  somewhere 
on  this  line.  Now  from  the  top  or  l)otto)n  of  the  chart  measure 
the  longitude,  and  with  this  space  in  the  dividers  lay  them  on  the 
line  drawn,  being  careful  in  regard  to  the  direction  in  which  the 


Chart  Illustrating  Cross  Bearings,  and  two  Bearings  of  one  Object, 
with  Course  and  Distance  Run  Between. 


longitude  is  increasing,  and  make  nnotlicr  mark;  tliis  will  be  the 
desired  position. 

When  drawing  lines  and    making  tcitiporary   marks  on  a  chart 
do  so  vci-y  liglitly,  so  that  llicy  may  easily  be  rubbed  ofl'. 

T(i  Flinl  llic  Ldlihnlr  iiitil  Loinjllinlr  of  a   I'Jdce. 
Measure  from  ibe  nearest   parallel   to  the  plaee  and  then  lay  the 
dividers  on  the  hititmle  abreast  and  read  the  degn'es  and  minutes; 


ClIAUT-WoKK.  22' 


this  will  be  the  latitude.  A'ext  measure  from  the  nearest  meridian 
to  the  same  place,  transfer  the  dividers  to  either  top  or  bottom  of 
chart,  read  the  degrees  and  minutes,  and  the  longitude  is  found. 
If  using  a  Polyconic  chart,  reference  must  be  made  to  the  interme- 
djate  scale  nearest  to  the  position,  and  the  latitude  must  not,  on 
any  account,  be  measured  from  the  side,  nor  the  longitude  from 
top  or  bottom.  The  reason  for  this  will  be  very  obvious  to  the  stu- 
dent if  a  Polyconic  chart  is  examined. 

Find  Ship's  Fosition  hy  Cross-Bearings. 

It  in  the  vicinity  of  the  land,  and  two  objects  be  distinctly  visi- 
ble at  one  and  the  same  time,  the  ship's  position  can  be  determined 
with  great  accuracy  if  care  is  exercised  in  taking  the  bearings,  cor- 
recting the  same  for  deviation  for  direction  of  ship's  head  and  plot- 
ting same  on  chart.     Thus: 

Take  the  two  bearings  as  close  together  as  possible,  apply  to 
them  the  deviation  for  Avhatever  the  ship  was  heading  at  the  time, 
allowing  East  to  the  right  and  West  to  the  left;  the  result  will  be 
the  Magnetic  Bearings.  Lay  the  rulers  on  the  magnetic  compass 
so  that  the  flat  edge  is  directly  over  the  center  and  also  over  the 
part  indicating  one  of  the  bearings;  advance  the  rulers  until  over 
the  point  whereof  the  bearing  was  taken  and  draw  a  line  •.  then  do 
the  same  with  the  second  bearing,  and  where  the  lines  intersect 
will  be  ship's  position. 

To  Find  Ship's  Position  hy  Two  Bearings  of  One  Point  with  the 
Assitstance  of  the  Course  and  Distance  Run  Between. 
Take  a  bearing  of  the  point  and  note  the  time  and  what  is  on  the 
patent  log  if  you  have  one  out;  keep  going  on  the  same  course 
until  the  bearing  has  altered  one  or  two  points,  and  then  take  an- 
other bearing  of  the  same  object;  correct  the  bearings  for  the  de- 
viation for  the  ship's  head  as  before  and  lay  them  on  the  chart; 
next  lay  the  ruler  over  the  magnetic  course  the  ship  is  steering, 
and  with  the  distance  the  ship  has  sailed  in  the  interval  between 
bearings  in  the  dividers,  move  the  rulers  until  the  legs  of  the  di- 
viders touch  the  bearings,  and  where  the  foot  of  the  dividers 
touches  the  second  bearing  will  be  the  ship's  position  at  the  time 
of  taking  the  second  or  last  bearing.  (This  method  requires  the 
use  of  both  hands,  the  left  moving  the  rulers  and  the  right  holding 
the  dividers.) 

There  is,  still  another  method,  as  follows: 

Lav  the  l)earino->   down   on  the  chart   as   before,   and   with  the 


328 


Taylor's  Modern   Xavigation. 


rulers  bring  the  course  over  to  any  part  of  the  bearings  and  draw 
a  line;  then  with  the  distance  traveled  in  the  interval  in  the  di- 
viders, place  one  foot  on  the  first  bearing  where  the  course-line 
crosses  it  and  measure  along  the  course  and  make  a  mark ;  now  lay 
the  rulers  on  first  bearing  and  advance  until  the  flat  edge  is  over 
this  mark,  and  draw  a  line  so  that  it  will  cut  the  second  bearing. 
This  method  will  also  give  the  ship's  position  at  time  of  taking 
the  second  bearing. 

To  Find  Ship's  Position  by  Four-Point  Bearing^  or  Double  the 
Bearing. 

This  very  handy  little  problem  is  of  the  greatest  practical  value 


Chart  Illustrating  the  Four  Point 
Problem  or  Double  the  Angle 

to  the  navigator  when  coasting,  for  by  it  the  distance  off  a  point 
may  be  found  without  recourse  to  a  chart. 

Take  a  bearing  of  a  point  when  it  is  four  points  from  ship's 
iiead,  namely,  four  ])()ints  off  the  bow;  note  wliat  is  on  the  patent 


C]iai;t-\\()KK.  229 


log  and  also  the  time;  proceed  on  course  without  changing  it  until 
the  object  is  directly  abeam.  The  distance  traveled  in  the  interval 
will  be  the  distance  off  wIumi  it  was  nhcam. 

It  will  bo  noticed  that  the  above  four-point  bearing  was  doubled 
to  eight  points  when  the  object  was  brought  abeam,  therefore  the 
problem  may  be  applied  to  two,  three,  or  three  and  a  half  points 
from  the  bow,  the  ship  steaming  on  her  course  until  the  angle  is 
doubled,  the  distance  traveled  being  the  distance  off  the  point. 

There  are  in  Bowditch  two  tables  for  the  above  purpose.  By 
reference  to  these  tables  and  by  paying  strict  attention  to  the  rules 
given  they  will  be  found  to  be  of  considerable  benefit  when  coast- 
ing. It  is  not  necessary  to  explain  these  tables  here,  as  we  con- 
sider the  Bowditch  explanation  sufficiently  explicit. 

Current  Sailing. 

The  preceding  rules  given  to  find  the  course  to  steer,  it  should 
be  thoroughly  understood,  are  only  for  finding  the  course  in  locali- 
ties where  there  is  no  current,  and  as  there  are  very  few  places 
where  there  is  no  current,  it  stands  to  reason  that  some  method  must 
be  used  to  counteract  the  current  when  one  exists.  The  following 
explanation,  we  hope,  will  be  sufficiently  plain  to  the  ordinary, 
every-day  navigator,  so  that  this  dangerous  item  in  navigation  may 
be  overcome,  provided,  however,  that  the  direction  and  rate  of  cur- 
rent is  known. 

Authentic  information  in  regard  to  the  set  and  drift  of  ocean 
currents  may  be  found  on  the  pilot-charts  or  in  books  of  sailing 
directions,  or  maybe  from  the  navigator's  previous  experience;  but, 
no  matter  from  what  source  the  information  is  obtained,  due  re- 
gard must  be  paid  to  previous  w^eather  conditions,  as  quite  a  num- 
ber of  ocean  currents  are  influenced  by  wind,  and  depend  a  great 
deal  on  the  season,  temperature,  etc. 

The  navigator  should  not  confuse  ocean  currents  with  tidal  cur- 
rents, as  the  causes  of  the  two  are  quite  different,  but  the  method 
to  find  a  course  to  steer  in  order  to  counteract  either  one  or  the  other 
is  the  same. 

1.  If  the  current  is  setting  in  the  same  direction  as  the  vessel 
is  traveling,  the  speed  over  the  ground  will  be  the  sum  of  the  rate 
of  the  current  and  the  speed  of  the  ship. 

2.  If  the  current   is   setting   in   an   opposite   direction   to  the 


230  Taylor's   Modkrx   iSTAviGATiON. 

course  of  the  shiiD,  the  rate  of  progression  will  be  the  speed  of  ship 
minus  rate  of  current. 

3.  If  the  set  of  tlie  current  is  at  right  angles  to  course  of  ship, 
the  vessel's  speed  will  neither  be  accelerated  nor  retarded,  but  she 
will  be  driven  off  her  course.  To  counteract  the  effect  of  the  cur- 
rent, find  out  how  many  hours  it  will  take  the  vessel  to  make  a  cer- 
tain distance,  by  dividing  the  distance  by  the  speed  of  the  ship  per 
hour,  and  multiplying  the  result  by  the  rate  of  the  current  per 
hour;  this  will  give  the  total  amount  of  set.  jSText  lay  the  rulers 
over  the  direction  of  the  set  and  advance  them  over  to  the  point 
the  ship  is  steering  for,  and  draw  a  line  in  the  opposite  direction 
to  what  it  is  setting;  along  tliis  line  measure  with  the  divich'rs  tlie 
total  amount  of  set  and  make  a  mark;  now,  with  the  rulers  over 


ill  is  mark  and  the  point  of  departure,  move  them  until  the  flat 
edge  is  over  the  center  of  the  compass  and  read  the  course. 

4.  As  a  rule,  however,  the  current  is  not  always  so  obliging  as 
to  set  in  the  preceding  manner;  for  it  may  set  in  an  ()l)lique  direc- 
tion, as  follows: 

If  the  current  is  setting  so  as  to  catch  tlie  ship  abaft  the  beam, 
ii  will  increase  the  vessel's  speed,  and  at  the  same  time  will  drive 
her  off  her  course.  If  it  catches  her  anywlu>re  forward  of  tlie  l)eam, 
it  will  retard  her  speed,  and  at  ibe  same  time  set  her  off  her  course. 
Under  these  conditions  the  navigator  should  find  the  current  course 
after  the  following  manner.  ])aying  strict  attention  to  the  dia- 
gram accompanying  tlie  article. 

Draw  a  line  on  the  chart    from  the  ])lace  of  ship  to  the  place 


ClJAKT-WOKK.  -^31 


tile  ship  is  bound  to,  and  mark  the  point  of  departure  A  and  tlio 
point  to  which  the  ship  is  bound  B. 

From  A  draw  a  line  representing  the  set  of  the  current  and 
mark  it  C ;  on  this  line  AC  lay  off  the  amount  of  set  per  hour,  say 
for  about  three  or  six  hours ;  then  with  the  distance  the  ship  would 
sail  in  the  above  length  of  time  in  the  dividers,  place  one  foot  at 
C  and  describe  an  arc,,  cutting  the  first  line  drawn  at  D;  now  lay 
the  rulers  over  D  and  C,  move  them  over  to  the  compass,  and  the 
current  course  is  found.  The  distance  the  ship  will  make  good  in 
the  interval  will  be  from  A  to  D. 

To  Find  the  Compass  Course  to  Steer  to  Malcc  a  Magnetic  Course 
Taken  fro)n  a  Chart. 

It  will,  no  doubt,  be  remembered  that  the  rules  for  applying  the 
variation  and  deviation  to  the  true  and  magnetic  courses  have 
already  been  explained  in  a  previous  part  of  this  section,  yet,  al- 
though this  has  been  done,  there  still  remains  a  very  important 
item,  relating  to  the  selection  of  the  proper  deviation  to  apply  to  a 
magnetic  course  before  the  compass  course  is  found. 

It  should  be  borne  in  mind,  as  we  progress,  that  there  are  three 
kinds  of  courses,  namely,  the  True,  Magnetic,  and  Compass.  Some 
writers,  whose  authority  is  not  to  be  questioned,  use  the  term 
''Magnetic"  for  the  Compass  Course,  and  "Correct  Magnetic"  for 
what  the  compass  would  indicate  when  not  influenced  by  iron  in 
the  vicinity.  We  do  not  say  they  are  incorrect,  but  it  is  our  opinion 
that  the  terms  "Compass  Course"  and  "Compass  Bearing"  are  the 
best  terms  to  apply  to  anything  indicated  by  a  compass,  and  the 
simple  term  "Magnetic"  the  best  term  for  what  the  compass  would 
indicate  provided  it  had  no  deviation.  This  little  digression,  we 
hope,  will  be  pardoned,  as  we  consider  it  necessary  to  explain  the 
ambiguity  of  the  terms  as  used  in  different  books  on  the  subject. 
To  resume,  it  is  generally  considered  advisable  to  det.'rmine  tlu^ 
deviation  for  ship's  head  by  compass  as  frequently  as  possible,  the 
same  to  be  entered  in  a  book  kept  for  the  purpose,  or  if  the  vessel 
is  simply  a  coaster,  it  may  be  noted  on  a  card  and  hung  up  in 
some  convenient  place,  like  the  chart-house,  for  easy  reference. 
Sometimes  these  cards  have  the  magnetic  courses  marked  abreast  of 
the  direction  of  the  ship's  head.  This  is  all  very  well  when  coast- 
ing between  ports  not  very  widely  separated,  but  it  will  not  do  for 
a  vessel  that  makes  long  voyages. 


282  Taylor's  Modern'  Xayigatiox. 

Again,  sometimes,  but  very  rarely,  a  deviation-card  is  found 
giving  the  deviation  for  ship's  head  magnetic,  but  as  this  would 
be  of  nse  only  on  vessels  running  practically  on  the  same  courses 
and  in  the  same  locality,  day  in  and  day  out,  it  is  hardly  necessary 
to  give  it  more  than  passing  mention. 

If  the  student  will  turn  back  to  Napier's  Diagram  and  examine 
the  curves  drawn  thereon  and  reread  the  rules,  it  will  be  noticed 
that  if  the  space  is  measured  between  the  center  line  and  the  curve 
on  or  parallel  to  a  dotted  line,  the  deviation  is  found  for  ship's 
head  by  compass,  but  if  measured  on  or  parallel  to  a  plain  line 
the  deviation  is  found  for  ship's  head  magnetic.  The  difEerence 
between  the  two  amounts  of  deviation  will  be  considerable,  under 
certain  conditions,  especially  when  the  compass  has  large  errors, 
and  on  those  courses  where  the  deviation  changes  very  rapidly. 

It  is  therefore  of  the  utmost  importance  that  the  terms  "Devia- 
tion for  ship's  head  by  compass"  and  "Deviation  for  ship's  head 
magnetic"  be  thoroughly  understood,  for  ignorance  in  regard  to 
them  may  be  the  means  of  placing  the  ship  on  the  rocks.  As  an 
illustration,  let  us  suppose  the  ship  to  be  heading  North  by  com- 
pass, and  that  on  this  course  there  are  two  points  of  easterly  devia- 
tion. In  this  case  the  ship  would  be  heading  N.X.E.  magnetic ; 
and  if  it  were  required  to  steer  North  magnetic,  it  would  be  neces- 
.sary  to  steer  by  compass  N.N.W. 

Now.  as  the  deviation  is  governed  by  the  angle  the  compass- 
needle  makes  with  the  mass  of  iron  near  it.  or  in  other  words,  as 
it  depends  on  the  direction  of  the  ship's  head,  it  will,  no  doubt, 
he  easily  understood  that  the  deviation  for  North  by  compass  could 
not  be  the  deviation  for  North  magnetic,  for  the  reason  that  it  is 
necessary  to  place  the  ship's  head  by  compass  in  a  direction  to 
counteract  tlie  effect  of  the  deviation. 

Again,  take  the  case  of  a  vessel  sent  to  sea  on  a  clear  day,  the 
master  having  no  knowledge  of  the  deviation  of  his  standard  com- 
pass. As  soon  as  the  vessel  is  outsidt"  he  can  place  the  ship's  head 
on  the  magnetic  course,  take  an  azitmith  and  determine  the  devia- 
tion, then  apply  this  deviation  to  the  magnetic  course.  East  to  the 
left  and  West  to-  the  right,  and  the  result  will  be  an  approximate 
course.  Now  he  will  place  the  ship's  head  on  this  last  course,  take 
an  azimuth  and  again  find  the  deviation,  applying  this  last  devia- 
tion to  the  magnetic  course  again,  and  get  another  approximate 


Chart-Work.  'i'-V-^ 


course,  repeating  tliis  until,  no  matter  how  nuui\'  azimuths  are 
taken,  each  deviation  found  is  the  same.  This  will  prove  that  the 
?]iip  is  now  heading  on  the  desired  magnetic  course. 

The  foregoing  is  .simply  an  illustration,  for  we  hardly  expect 
that  any  master  would  be  so  foolhardy  as  to  proceed  to  sea  with- 
out some  knowledge  of  the  deviation  of  one,  at  least,  of  the  vessel's 
compasses.  If  he  does  so,  the  sooner  he  is  relieved  of  his  command, 
the  better  for  all  concerned. 

The  proper  mode  of  procedure  to  determine  the  correct  amount 
of  deviation  to  apply  to  the  magnetic  course  to  obtain  the  compasi; 
course  to  steer  is  as  follows: 

From  a  table  of  deviation,  (or,  better  still,  from  the  regular 
book  containing  the  compass  records),  take  the  deviation  for  the 
magnetic  course  and  apply  East  to  the  left  and  West  to  the  right; 
the  result  will  be  the  approximate  course.  Enter  table  again  with 
this  approximate  course,  take  the  corresponding  deviation,  apply 
this  to  the  magnetic  course  and  obtain  another  approximate  course ; 
enter  table  again  with  this  last  approximate  course,  repeating  the 
operation  until  the  deviations  and  the  course  are  always  found  to 
be  the  same,  no  matter  how  often  the  table  is  entered.  The  result 
will  be  the  proper  deviation,  and  the  correct  course  to  steer  by  the 
compass. 

If  it  is  required  to  correct  a  course  by  compass  to  find  the  mag- 
netic course,  it  would  only  be  necessary  to  enter  the  table  and 
take  therefrom  the  deviation  at  sight,  as  the  table  is  given  for 
sliip's  head  by  compass. 

The  following  questions  are  worked  on  Chart  Xo.  1000,  from 
Cape  Sable  to  Cape  Hatteras : 

Examples   for  I'mctice    in   Finding    the   True    Course,   Magnetic 
Course,  and  Distance  between  Two  Places. 

From  Sandy  Hook  light- vessel  to  Barnegat? 

AnsAver.— T.  co.  S.  16°  W.;  mag.  co.  S.  26°  W.;  dist.  44  miles. 

From  Barnegat  to  Shinnecock? 

Answer.— T.  co.  X.  49°  E.;  mag.  co.  X.  59°  E.;  dist.  99  miles. 

From  Shinnecock  to  Xantucket  Shoal  light-ship? 

Answer.— T.  co.  S.  84°  E. ;  mag.  co.S.  71°  E.;  dist.  133  miles. 


234  Taylor's  ]\Ioderx   Xavigatiox. 

From  Xantucket  Shoal  light-ship  to  Tucker  Beach  light? 
Answer.— T.  co.  S.  73°  W. ;  mag.  co.  S.  83°  W.;  dist.  227  miles. 

From  Cape  Ann  to  Cape  St.  j\[ary  ? 

Answer.— T.  co.  X.  65°yoE.:  mag.  co.  X.  811/:.°  E. ;  dist.  200 
miles. 

From  Cape  Cod  to  Seguin  Island? 

Answer.— T.  co.  N.  8°  E. ;  mag.  co.  N.  24°  E. ;  dist.  101  miles. 

From  Cape  Elizaheth  to  Seal  Island,  Nova  Scotia? 

Answer.— T.  co.  S.  86°  E. ;  mag.  co.  S.  71°  E.;  dist.  182>{.  miles. 

Example. 

What  is  the  magnetic  course  and  distance  from  Brier  Island  to 
Boon  Island? 

Answer.— Mag.  co.  S.  851/0°  W.;  dist.  190  miles. 

Ship's  head  on  the  magnetic  course  found,  Mount  Desert  Eock 
bore  magnetic  !N".E.XE.i/2E.  and  Matinicus  Rock  bore  magnetic 
N'.W.^W.    What  was  the  ship's  position  by  cross-bearings ''' 

Answer.— Lat.  43°  41'  N".;  long.  68°  32'  W. 

Ship  still  heading  on  the  magnetic  course  found,  Monhegan 
Island  bore  magnetic  JST.N.W.,  and  after  continuing  on  same  course 
12  miles  it  bore  magnetic  X.E.  What  was  the  ship's  position  at 
the  time  of  taking  the  second  bearing,  and  her  distance  off  Mon- 
hegan Island  ? 

Answer.— Lat.  43°  34'  N.;  long.  69°  27'  W.;  dist.  off,  13  miles. 

And  suppose  there  was  a  current  setting  the  ship  to  the  S.E. 
magnetic  at  the  rate  of  one  mile  an  hour,  ship  steaming  12  miles 
an  hour,  what  magnetic  course  would  you  steer  from  Brier  Island 
to  Boon  Island,  and  what  distance  would  the  ship  make  good  in 
four  hours  ? 

Answer. — Cur.  co.  S.  89°  W.  Distance  made  good  in  four  hours. 
45  miles. 

Find   the  magnetic  coui'se  and   distance    from   Cannet   Rock   in 
order  to  pass  three  miles  off  Seal  Island,  Nova  Scotia. 
Answer. — Magnetic  co.  S.  9°  E. ;  dist.  74  miles. 
Slii])'s   liead   on    the   niai^iietic  course    found.   Brier    Island   bore 


Chaht   Work. 


235 


iiuigiu'tie  E.Xi^-V2N-,  find  Cape  St.  Mary  bore  magnetic  S.E.X 
E.i^E.    What  was  the  ship's  position  by  eross-bcarings? 

Answer.— Lat.  44°  8'  30"  N. ;   hmg.  (K^  3(i'  W. 

Ship  still  heading  on  magnetic  course  found,.  Cape  St.  Mary 
bore  magnetic  E.l^S.,  and  after  continuing  on  same  course  10 
miles  it  bore  magnetic  N.E.i/oN.  What  was  the  ship's  position 
at  the  time  of  taking  the  second  bearing,  and  her  distance  off  Cape 
St.  Mary? 

Answer.— Lat.  43°  54'  N.;  long.  (i()°  19'  30"  W.  Dist.  off,  12 
miles. 

DEYIATION-CARD. 

(To  be  used  in  all  of  the  chart-questions  given  in  this  book.) 


Ship's  Head  by  Compass. 

Deviation. 

Ship's  Head  by  Compass. 

Deviation. 

North 

5°  W. 

South 

4°   W. 

N.XE. 

8°  W. 

S.XW. 

2-  E. 

N.N.E. 

9°  W. 

s.s.w. 

9°  E. 

N.E.XN. 

10°  W. 

s.w.xs. 

15°  E. 

NE. 

11°  W. 

s.w. 

22°  E. 

N.E.XE. 

12°  W. 

s.w.xw. 

21°  E. 

E.N.E. 

14°  W. 

w.s.w. 

20°  E. 

E.XN. 

1B°  W. 

w.xs. 

19°  E. 

East 

17°  W. 

West 

18°  E. 

E.XS. 

lf)°  W. 

W.XN. 

15°  E. 

E.S.E. 

1B°  W. 

W.N.W. 

11°  E. 

S.E.XE. 

14°  W. 

N.W.XW. 

8°  E. 

S.E. 

13°  W. 

N.W. 

4-^  E. 

S.E.XS. 

11°  W. 

N.W.XN. 

1°  E. 

S.S.E. 

1)°  W. 

N.N.W. 

2°  W. 

S.XE. 

7°  W. 

N.XW. 

3°  W. 

Examples  in  Fuidiinj  the  I' ropey  Deviation  to  Apply  to  a  Magnetic 
Course  to  Obtain  a  Correet  Compass  Course. 

Mag.  CO.  S.W.XW'.  gives  from  table  of  deviations  2U°  E. 
Mag.  CO.  S.  51°     W. 
Dev.  21i°  E. 

S.  29^°  W.  1st  approx.  CO.  S.W.  XS.^S.  gives  dev.  13^°  E. 


Mag.  CO.  S.  51°    W. 
Dev.  13^°  E. 

S.  37^°  W.  2d  approx.  co.  S.W.|S.  gives  dev.  16°  45'  E. 


236  Taylor's  Modern  Navigation. 

Mag.  CO.  S.  51°         W. 
Dev.  16°  45'  E. 

S.  34°  15'  W.  3d  approx.  co.  S.W.XS.  gives  dev.  15°  E. 

Mag.  CO.  S.  51°  W. 
Dev.  15     E. 

S.  36°  W.  4th  approx.  co.  S.W.|S. 

It  will  be  noticed  that  the  amounts  of  deviation  alternate ;  there- 
fore take  the  mean  of  the  two  last  amounts  as  the  proper  deviation 
to  apply  to  the  magnetic  course  to  obtain  the  correct  compass  course 
to  steer,  and  if  it  is  required  to  prove  it,  simply  enter  the  devia- 
tion table  again  and  it  will  be  found  to  repeat  itself.    Thus : — 


Dev. 

16°  45  E. 

Dev. 

15  00  E. 

2)31  45 

15°  52'  E. 

Mag.  CO. 

S.  51°  00'  W. 

Dev. 

15  52  E. 

S.  35°  08'  W.  compass  course  to  steer. 

In  actual  practice,  and  with  a  compass  with  a  small  error,  the 
operation  will  not  be  so  long. 

Mag.  CO.  S.W.XS.^S.  gives  dev.  12°  E. 
Mag.  CO.  S.  28°  W. 
Dev.  12    E. 

S.  16°  W.  1st  approx.  co.  S.  X  \V.4  W.  gives  5.^°  E.  dev. 

Mag.  CO.  S.  28°     W. 
Dev.  5^°  E. 

S.  224°  W.  2d  approx.  co.  S.S.W.  gives  9°  E.  dev. 

Mag.  CO.  S.  28°  W. 
Dev.  9°  E. 

S.  19°  W.  3d  approx.  co.  S.XW.f  W.  gives  7°  E.  dev. 

Mag.  CO.  S.  28°  W. 
Dev.  7°  E. 

S.  21°  \V.  4th  approx.  co.  S.XW.^W. 


Chart  Work.  237 


After  this,  no  matter  how  many  times  the  deviation  table  is  en- 
tered, ?°  E.  deviation  will  be  found;  therefore  it  must  be  the 
proper  deviation  to  use. 

Mag.  CO.  E.XS.  gives  dev.  16°  W. 
Mag.  Co.  S.  79°  E. 
Dev.  16    W. 

S.  63°  E.  1st  approx.  co.  S.E.XE.^  E.  gives  dev.  15°  W. 

Mag.  CO.  S.  79°  E. 
Dev.  15    W. 

S.  64°  E.  2d  approx.  co.  S.E.XE.^  E.  gives  dev.  15^°  W. 

Mag.  CO.  S.  79°  E. 
Dev.  15^  W. 

S.  63^  °E.    the  correct  compass  course  to  steer,  the  de- 
viation being  15^°  W. 

When  working  the  following  chart  questions,  all  bearings  must 
be  corrected  for  the  deviation  of  ship's  head. 

Find  the  compass  course  and  distance  from  Nantucket  Shoal 
light-vessel  to  Navesink.    T.  co.  S.  87°  W. 

Mag.  CO.  N.  83°  \V.  W.^S. 

Dev.  184  E. 

N.  lOli  W. 
180 


S.  78^°  W.  1st  approx.  co.  W.XS. 

Mag.  CO.     N.  83°  W. 
Dev.  19    E. 

N.  102    W. 

180 

Comp.  CO.  S.  78°  W.    Dist.  201  miles;  dev.  19°  E. 

Ship  heading  on  the  compass  course  found,  Shinnccock  bore  by 
compass  N.E.^N.,  and  Fire  Island  light  bore  by  compass  W.X 
X.14X.    What  was  the  ship's  position  by  cross-bearings? 

Shinnecock.  Fire  Island. 

N.E.I  N.  =  N.  36°  34'  E.         W.XN.iN.  =  N.  75°  56' W. 
Dev.  19    00   E.         Dev.  19    00  E. 


N.E.XE.  =  N.  55°  34'  E.  N.W.XW  =  N.56°  56'  W. 

Answer.— Lat.  40°  32'  N. ;  long.  72°  56'  W. 


238  Taylor's  Modern   Xavigatiox. 

Ship  still  heading  on  the  compass  course  found,  Fire  Island 
bore  by  compass  X.XW.%W.,  and  after  continuing  on  the  same 
course  18  miles  it  bore  by  compass  N.E.X-N^-%^'-  What  was  the 
ship's  position  at  the  time  of  taking  the  second  bearing,  and  her 
distance  off  Fire  Island? 

1st  Bearing.  2d  Bearing. 

N.XW.|W.  =  N.  19°  41'  W.         N.E.XN.|N.  =  N.  25°  19'  E, 

19    00  E. 

N.  44°  19'  E 
3°   23'  W.     Dist.  off,  121/2 


And  sujDposing  there  was  a  current  setting  the  ship  to  the  Xorth 
magnetic  at  the  rate  of  i/o  mile  an  hour,  ship  steaming  10  miles 
an  hour,  what  compass  course  would  you  steer  from  Xantucket 
light-vessel  to  Navesink? 

The  distance  of  201  miles  divided  by  10  miles  will  give  20  hours, 
the  length  of  time  the  vessel  will  take  to  travel  the  distance.  This. 
20  hours  multiplied  by  the  rate  of  current  will  give  10  miles  as 
the  total  amount  of  set;  therefore  the  magnetic  course  to  counter- 
act the  effect  will  be: 


Dev. 

.^N 

= 

19 

00 

E. 

w. 

Dev. 

N.  W 

N.  38° 

41' 

N.E, 

Answer. — 

-Lat 

.  40°  : 

27' 

^^; 

long. 

73° 

miles. 

Mag.  CO.    N.    87°        W.  =  W.iN. 
Dev.  17°  15'  E. 


N.  104°  15'  W. 
180    OC 


S.    75°  45'  W.  lst>pprox.  co.  W.XS.i  S. 


Mag.  CO.    N.     87°        W. 
Dev.  19    15'  E. 

N.  106^5'  W. 
180 


S.     73°  45'  W.  2d  approx.  co.  W.XS.^  S. 


Mag.  CO.  N.     87°  W. 
Dev.  19    E. 

N.  10fi°  W. 
180 


S.    74°  W.  Current  co.  to  steer  by  compas! 


Chart-Work.  230 


It  will  be  noticed  here  that  all  bearings  are  by  compass;  there- 
fore they  must  be  corrected  for  the  deviation  of  ship's  head  namely, 
19°  E.,  allowing  East  to  the  right  and  West  to  the  left,  before  they 
are  placed  on  the  chart.  If  the  chart  had  been  true,  the  variation 
also  would  have  had  to  be  applied  in  the  same  manner,  but  as  it 
io  a  magnetic  chart  it  is  necessary  to  apply  only  the  deviation  to 
the  compass-bearings  to  obtain  magnetic  bearings. 

Example. 

Find  the  compass  course  and  distance  from  ^linot's  Ledge  to 
Seguin  Island. 

Answer.— Mag.  eo.  X.  ^3°  E. ;  dev.  12°  W. :  eonip.  co.  X.  00°  E. ; 
dist.  97  miles. 

Ship's  head  on  the  compass  course  found,  Isles  of  Shoals  light 
bore  by  compass  X.14W.  and  Boon  Island  bore  by  compass  X.X.E. 
What  was  the  ship's  position  by  cross-bearings  ? 

Answer.— Lat  42°  43'  30"  X.;  long.  70°  26'  W. 

Ship  still  heading  on  the  compass  course  found,  Cape  Elizabeth 
bore  by  compass  X.XE.%E.,  and  after  continuing  on  same  course 
11  miles  it  bore  by  compass  Xorth.  What  was  the  ship's  position 
at  the  time  of  taking  the  second  bearing,  and  her  distance  off  Cape 
Elizabeth  ? 

Answer.— Lat.  43°  18'  X.;  long.  69°  59'  W.  Dist.  off,  181/2 
miles. 

And  supposing  there  was  a  current  setting  the  ship  to  the  X.X. 
W.  magnetic  at  the  rate  of  li/o  miles  an  hour,  ship  sailing  12  miles 
an  hour,  what  compass  course  would  you  steer,  and  wliat  distance 
would  the  ship  make  good  in  five  hours? 

Answer.— Mag.  co.  X.  49°  E. ;  dev.  13°  W.;  comp.  co.  X.  62°  E. 
Dist.  made  good,  63  miles. 

J'J.raiii  pie. 

Find  the  compass  course  and  distance  from  Barnegat  to  Gay 
Head. 

Answer.— Comp.  co.  X.  85°  E.;  dev.  17°  W.   Dist.  178  miles. 

Ship's  head  on  the  comi)ass  course  found.  Shinnecoek  bore  l»y 
compass  W.X.W.  and  Montauk  bore  by  eom])ass  X.E.XE.14E. 
What  was  the  ship's  position  by  cross-bearings? 

Answer.— Lat.  40°  53'  X. :  long.  72°  01'  W. 


240  Taylor's  Modern  Navigation. 

ShiiD  still  heading  on  the  compass  course  found,  Block  Island 
bore  by  compass  ISr.E.i4N".,  and  after  continuing  on  same  course 
G  miles  it  bore  by  compass  N.i^W.  What  was  the  ship's  position 
at  the  time  of  taking  the  second  bearing,  and  her  distance  off 
Block  Island? 

Answer.— Lat.  41°  4'  30"  N.;  long.  71°  29'  W.  Dist.  off,  6I/2 
miles. 

And  suppose  there  was  a  current  setting  the  ship  to  the  North 
magnetic  at  the  rate  of  I14  miles  an  hour,  ship  steaming  12  miles 
an  hour,  what  compass  course  would  you  steer,  and  what  distance 
would  the  ship  make  good  in  six  hours  ? 

Answer.— Mag.  co.  N.  73°  E. ;  dev.  17°  W. ;  comp.  co.  East,  Dist. 
made  good.  73  miles. 

Example. 

Find  the  compass  course  and  distance  from  Shinnecock  to  Fen- 
wick  Island  Shoal  light-vessel. 

Answer.— Mag.  co.  S.  48°  W. ;  dev.  14°  E. ;  comp.  co.  S.  34°  W. 
Dist.  182  miles. 

Ship's  head  on  the  compass  course  found,  Absecon  light  bore 
by  compass  N.W.%N.,  and  N.E.  end  of  Five-fathom  Bank  light- 
vessel  bore  by  compass  S.W.i/oW.  What  was  the  ship's  position 
by  cross-bearings  ? 

Answer.— Lat.  39°  6'  N.;  long.  74°  14'  W. 

Ship  still  heading  on  the  compass  course  found.  Cape  May  bore 
by  compass  W.XN.1/4N.,  and  after  continuing  on  same  course 
19  miles  it  bore  by  compass  N.W.X^.  What  was  the  ship's 
position  at  the  time  of  taking  the  second  bearing,  and  her  dis- 
tance off  Cape  May? 

Answer.- Lat.  38°  32'  N.;  long.  74°  43'  W.  Dist.  off,  26 
miles. 

And  suppose  there  was  a  current  setting  the  ship  to  the  N.N.W. 
magnetic  at  the  rate  of  %  of  a  mile  in  one  hour,  ship  sailing  9 
miles  an  hour,  what  compass  course  would  you  steer  from  Shinne- 
cock to  Fenwick  Island  Shoal  light-vessel? 

Answer.- Mag.  co.  S.  43°  W. ;  dev.  13°  E.;  comp.  co.  S.  30°  W. 

('hart-Questions  Worl-ed  on  Chart  No.  5002,  Pacific  Coast. 
Example. 

Find  the  compass  course  and  distance  from  Point  Reyes  to  Point 
Sur. 


Chart- Work.  2il 


Answer.— Cornp.  co.  S.  34°  E.:  dev.  11°  W.    Dist.  115  miles. 

Ship's  head  on  the  compass  course  found,  Farallone?  light  bore 
by  compass  W.^N.,  and  Point  Bonita  bore  by  compass  X.E.X^"- 
What  was  the  ship's  position  by  cross-bearings  ? 

Answer.— Lat.  37°  38'  N.:  long.  122°  43'  W. 

Ship  still  heading  on  the  compass  course  found,  Monterey  light 
bore  by  compass  E.XS.,  and  after  continuing  on  same  course  8 
miles  it  bore  by  compass  X.E.  What  was  the  ship's  position  at  the 
time  of  taking  the  second  bearing,  and  her  distance  off  Monterey 
light  ? 

Answer.— Lat.  3(i°  33'  30"  X.;  long.  122°  2'  W.  Dist.  off,  7 
)niles. 

And  supposing  thore  was  a  current  setting  the  ship  to  the  E.S.E. 
magnetic  at  the  rate  of  IV2  miles  an  hour,  ship  sailing  10  miles 
an  hour,  what  compass  course  would  you  steer  from  Point  Keyes 
to  Point  Sur,  and  what  distance  would  the  ship  make  good  in  9 
hours  ? 

Answer.— Comp.  eo.  S.  30°  30'  E. ;  dev.  10°  30'  W.  Dist.  made 
good.  103  miles. 

Example. 

Find  the  com])ass  course  and  distance  from  2  miles  off  Point 
Fermin  to  Point   Conception. 

Answer.— Comp.  co.  S.  80°  W.:  dev.  19°  E.    Dist.  118  miles. 

Ship's  head  on  the  compass  course  found.  Point  Hueneme  bore 
by  compass  N.E.XN.,  and  Anacapa  Island  bore  by  compass 
South,  what  was  the  ship's  position  by  cross-bearings? 

Answer.— Lat.  34°  6'  X.;  long.  119°  21'  W. 

Ship  still  heading  on  the  compass  course  found,  Santa  Barbara 
light  bore  by  compass  X.W.14X.,  and  after  continuing  on  the 
same  course  9  miles  it  Ix^rc  l)y  compass  X.XE.V4E.  What  was 
tlie  ship's  position  at  the  time  of  taking  the  second  bearing,  and 
her  distance  off  Santa  Barbara  light? 

Answer.- Lat.  34°  17'  X.;  long.  119°  52'  W.  Dist.  off.  10 
miles. 

And  suppose  there  was  a  current  setting  the  ship  to  the  E.X.E. 
magnetic  at  the  rate  of  one  mile  an  hour,  ship  steaming  10  miles 
an  hour,  what  compass  course  would  you  steer,  from  2  miles  off 
Point  Fermin  to  Point  Conception,  and  what  distance  would  the 
ship  make  good  in  seven  hours? 

Answer.— Comp.  co.  S.  77°  W. ;  dev.  19°  E.  Dist.  made  good,  64 
miles. 

Taylor's  Mod.   Nav.   16. 


242  Taylor's  Modern  Xavkutiox. 


Example. 
Find  the  compass  course  and  distance  from  3  miles  ofE  Point 
Arena  to  Point  Eeyes. 

Answer.— Comp.  co.  S.  38°  E.;  dev.  12°  W.   Dist.  6G1/0  miles. 

Ship's  head  on  the  compass  course  found,  Table  Mountain  bore 
by  compass  N.XE.i^E.,  and  Ross  Mountain  bore  by  C(unpass 
N.E.i^E.    What  was  the  ship's  position  by  cross-bearings? 

Answer.— Lat.  38°  24'  N.;  long.  123°  19'  W. 

Ship  still  heading  on  the  compass  course  found.  Bodega  Head 
bore  by  compass  E.I/2N.,  and  after  continuing  on  same  course  11 
miles  it  bore  by  compass  X.E.XN.3/4X.  What  was  the  ship's 
position  at  the  time  of  taking  the  second  bearing  ? 

Answer.— Lat.  38°  9'  N.;  long.  123°  10'  W. 

And  suppose  there  was  a  current  setting  the  ship  to  the  X.PLXX- 
magnetic  at  the  rate  of  two  miles  an  hour,  ship  steaming  8 
miles  an  hour,  what  compass  course  would  yon  steer,  from  3  miles 
off  Point  Arena  to  Point  Reyes,  and  what  distance  would  the  ship 
make  good  in  8  hours? 

Answer.— Comp.  co.  S.  26°  E. ;  dev.  10°  W.  Dist.  made  good. 
601/0  miles. 

Excuiiple. 

Find  the  compass  course  and  distance  from  Point  Arguello  to 
Piedras  Blancas. 

Answer.— Comp.  co.  N.  45°  W.;  dev.  4°  E.    Dist.  72  miles. 

Ship's  head  on  the  compass  course  found,  Port  Harford  bore  by 
compass  X.ysE.,  and  Point  Sal  bore  by  compass  E.XS.  What 
was  the  ship's  position  by  cross-bearings? 

Answer.— Lat.  34°  59'  N.;  long.  120°  50'  \V. 

Ship  still  heading  on  the  compass  course  found,  Port  Harford 
l)ore  by  compass  E.XN.14N.,  and  after  continuing  on  sann^ 
course  7  miles  it  bore  by  compass  E.34S.  What  was  the  ship's 
position  at  the  time  of  taking  the  second  bearing,  and  her  distance 
off  Port  Harford  ? 

Answer.— Lat.  35°  16'  N. ;  long.  121°  2'  W.     Dist.  olT,  16  miles. 

And  supposing  there  was  a  current  setting  the  shi])  to  the  East 
magnetic  at  the  rate  of  IVo  miles  an  hour,  ship  steaming  12  miles 


Chart-Work.  243 


<m  Jiour.  what  compass  ciiirsc  would  you  steer  from  Point  Arguello 
to  Piedras  Blanca?? 

Answer. — Comp.  co.  N.  52°  W. ;  dev.  G°  E. 

Example. 

Find  the  compass  course  and  distance  from  Point  Huenemo  to 
Point  Loma. 

Answer.— Comp.  co.  S.  48°  30'  E. ;  dev.  13°  30'  W.  Dist.  134 
miles. 

Ship's  head  on  the  compass  course  found,  Point  Dnmc  bore  by 
compass  X.i/iW.,  and  Saddle  Mountain  bore  by  compass  X.E.X 
X.14X".    What  was  the  ship's  position  by  cross-bearings? 

Answer.— Lat.  33°  50'  X.;   long.  118°  47'  30"  W. 

Ship  still  heading  on  the  compass  course  found,  Point  Fermin 
bore  by  compass  N.E.XE.i^E..  and  after  continuin.u-  on  same 
course  5  miles  it  bore  by  compass  X.E.X X-'*^X-  ^Vhat  was  the 
ship's  position,  and  her  distance  off  Point  Fermin? 

Answer.— Lat.  33°  34'  N.;  long.  118°  23'  W.    Dist.  off,  9  miles. 

And  suppose  there  was  a  current  setting  the  ship  to  the  X.X.E. 
magnetic  at  the  rate  of  one  mile  an  hour,  ship  steaming  8  miles  an 
hour,  what  compass  course  would  you  steer  from  Point  Hueneme 
to  Point  Loma? 

Answer.— Comp.  co.  S.  43°  30'  E.;  dev.  12°  30'  E. 

KEMAEKS  RELATING  TO  THE  CHART-QUESTIOXS,  AND 

OTHER  MATTERS  IN  REGARD  TO  COAST 

XAVIGATIOX. 

It  will  be  noticed,  when  working  the  various  examples  on  the 
chart,  that  the  ship  is  found  to  be  in  a  different  position  from  that 
intended  by  steering  the  course.  This  is  to  show  the  principle  of 
finding  ship's  position  by  the  bearings  taken:  Init  in  actual  practice 
it  would  be  necessary  to  alter  the  course  whenever  the  ship  is  found 
to  be  inside  or  outside  of  her  proper  position.  This  has  not  been 
done  in  the  examples,  for  the  reason  that  it  would  make  the  exam- 
ples too  lengthy  and  confusing  for  the  student. 

Before  giving  the  chart-questions  we  have  given  a  few  examples 
regarding  the  finding  of  the  proper  deviation  to  apply  to  the  mag- 


24:4  Taylor's  Moderx  Xavigatiox. 

netic  course  to  obtain  the  compass  course  to  steer.  They  are  ex- 
treme cases,  aud  are  used  to  serve  the  purpose  of  illustration.  The 
deviation  so  found  and  applied  to  the  magnetic  course  must  also 
be  applied  to  the  compass-bearings,  allowing  East  to  the  right  and 
West  to  the  left,  to  convert  the  compass-bearings  into  magnetic 
before  placing  them  on  the  chart.  The  reason  is  obvious,  for,  as 
deviation  is  governed  by  the  direction  of  the  ship's  head,  all  bear- 
ings taken  with  ship's  head  in  a  certain  direction  will  be  affected 
to  the  amount  of  deviation  for  the  direction  of  ship's  head. 

When  coasting,  it  is  of  the  utmost  importance  to  prove  the  ves- 
sel's position  by  utilizing  hearings  as  often  as  an  opportunity  pre- 
sents itself;  and  although  navigation  is  an  exact  science,  still,  for 
numerous  reasons,  such  as  bad  steering,  incorrectly  estimating  the 
amount  of  leeway,  send  and  strength  of  sea,  unknown  currents,  or 
sudden  and  erratic  changes  in  deviation,  etc.,  the  practice  of  navi- 
gation is  far  from  being  exact.  Knowing  this,  the  navigator  should 
be  extremely  careful,  and  should  not  let  any  opportunity  pass  by 
of  verifying  the  ship's  position  by  bearings  of  the  l?nd.  and  when 
approaching  coasts  where  the  charts  are  not  reliable  recourse  must 
be  had  to  the  lead  and  lookout. 

When  navigating  in  a  fog,  it  should  be  thoroughly  understood 
that  one  cast  of  the  lead  is  of  no  value  when  wishing  to  locate  the 
position  of  the  ship,  as  it  simply  gives  the  depth  of  water,  and 
nothing  else;  but  if  a  string  of  soundings  is  taken  at  regular  in- 
tervals, and  if  the  depths  found  by  the  lead  are  reduced  to  those 
found  on  the  chart,  these,  in  conjunction  with  the  nature  of  the 
bottom,  brought  up  on  the  "arming"  of  the  lead,  will  materially 
assist  in  determining  the  place  of  ship. 

Thus,  supposing  a  vessel  to  be  approaching  Sandy  Hook  from 
the  southward,  the  weather  foggy,  and  the  master,  being  doubtful 
of  his  position,  should  take  a  cast  of  the  lead  and  find  14  fathoms 
when  reduced  to  the  soundings  on  the  chart,  with  a  black  and  white 
sandy  bottom:  this  would  place  the  ship  anywhere  from  20  to  26 
miles  off  Barnegat.  But  if  the  ship  should  sail  North  magnetic  for 
()  miles,  and  another  cast  be  taken,  and  the  depth  found  is  20  fath- 
oms, and,  after  sailing  another  six  miles,  19  fathoms  is  found,  it 
will  prove  that  the  ship  is  iital-i\ng  X.  4°  E.  magnetic,  and  at  time 
of  last  cast  she  must  have  been  about  19  miles  ofE  Sea  Girt  light. 
To  verify  tliis.  the  master  should  keep  her  going  about  3  miles 
farther,  and  if  lie  then  find  37  fathoms,  he  may  consider  that  he 
hail  .1  fair  kiiowlcilo*.  of  lii,<  pdsifion  at  tlu^  time  of  taking  the  last 


Chart  Work.  245 


cast,  and  from  this  position  he  should  steer  about  N.  15°  W.  mag- 
netic, proceeding  slowly  and  using  the  lead  at  frequent  intervals 
until  the  fog-signal  on  Sandy  Hook  light-vessel  is  distinctly 
heard. 

It  should  be  borne  in  mind,  however,  that  the  state  of  the  tide, 
if  ebb  or  flood,  must  be  seriously  taken  into  consideration ;  for  if  it 
had  been  a  strong  flood-tide  in  the  above  case,  and  the  same  was  not 
allowed  for,  in  all  probability  the  navigator  would  have  found  his 
ship  over  towards  the  Navesink,  and  out  of  hearing  of  the  signal  on 
Sandy  Hook  light-vessel,  and  may  be  able  to  save  tlie  vessel  Troiu 
going  ashore  only  by  strict  attention  to  the  lead. 

Listening  for  a  Signal  During  a  Fog. 
There  is  an  exceedingly  important  point  in  regard  to  ''picking 
up"  a  fog-signal  during  a  fog  that  is  very  necessary  for  seamen  to 
understand,  and  that  very  few  know ;  therefore  we  are  sure  that  the 
following  will  be  of  considerable  interest. 

To  say  that  sound  in  a  fog  is  very  misleading  is  to  use  a  very 
mild  term,  especially  when  its  direction  from  the  ship  is  required. 
All  seamen  know  from  experience  that  the  sound  may  seem  to 
come  from  a  place  on  the  starboard  bow,  and  afterwards  it  may  be 
proved  that  it  was  on  the  port  bow.  For  instance,  how  many  times 
has  it  occurred,  when  near  a  signal,  that  it  could  not  be  heard,  and 
the  weather  clearing,  the  ship  was  found  to  be  in  close  proximity 
to  the  station,  and  still  the  signal  could  not  be  heard?  This  has 
occurred  very  often,  and  navigators  have  complained  to  the  light- 
house authorities  that  the  signal  was  not  in  operation,  and  yet  af- 
terwards it  was  proved  to  have  been  working.  The  question  is, 
then,  "Why  was  it  not  heard  ?"     This  I  will  endeavor  to  show. 

The  formation  of  the  land  at  the  back  of  the  station  may  be  such 
that  the  volume  of  sound  is  thrown  in  one  particular  direction,  and 
over  a  comparatively  small  arc  of  the  horizon,  making  it  impossible 
for  the  signal  to  be  heard,  although  the  ship  is  theoretically  within 
range  of  the  sound. 

Wind,  also,  may  have  an  effect,  and  it  would  be  generally  sup- 
posed that  if  to  the  leeward  of  the  station,  the  signal  would  be 
heard  with  greater  clearness  and  at  a  greater  distance  than  if  to 
windward.  This  is  not  always  the  case;  for  sometimes  a  signal 
may  be  very  distinct  when  the  ship  is  to  windward,  and  compara- 
tively faint  to  leeward.  We  opine  that  the  reason  of  this  is  to  be 
found  in  the  conformation  of  the  land  at  the  back  of  th(^  station, 
which  acts  as  a  sounding-board,  as  before  stated. 


;;4(j  Taylor's  ^Moderx  Xavigatiox. 

Again,  sound  will  reljound  like  a  rii1)bfr  ball  thrown  on  the 
ground  at  an  angle  of  about  45° ;  the  first  bound  will  be  quite  great, 
the  next  smaller,  and  so  on.  Now,  supposing  the  ship  to  be  close 
in  to  the  station,  the  sound  may  bound  clear  over  the  ship,  and 
although  she  may  be  within  range,  the  signal  may  not  be  heard,  but 
if  she  were  a  little  farther  out,  it  might  be  heard,  and  if  a  good 
distance  out,  it  might  be  heard  very  clearly  ;  which  proves  that  a  ve>- 
sel  may  be  close  in  and  still  not  hear  a  signal,  although  it  is  in 
operation.  This  therefore  exonerates  the  lighthouse  people  from 
the  imputation  of  carelessness  among  their  employees.  The  best 
plan,  when  listening  for  a  signal,  would  therefore  be  to  have  a  man 
as  high  up  on  the  mast  as  possible  to  listen,  for  the  masthead  may 
enter  the  zone  of  sound  quite  a  long  time  before  the  signal  is  heard 
on  deck.  This  may  not  always  be  the  case,  but  we  advise  the  navi- 
gator to  try  the  plan  suggested,  for  the  old-fashioned  method  of 
placing  the  ear  to  the  deck  is  out  of  date.  It  may  be  used  to  hear 
a  train  approaching,  but  there  are  no  iron  rails  on  the  ocean. 

The  preceding  was  inspired  by  reading  the  reports  of  investiga- 
tions made  by  the  United  States  government,  and  by  my  own  and 
other  navigators'  experience,  and  it  is  plainly  the  duty  of  the  navi- 
gator to  exercise  caution,  and  never  to  neglect  the  lead,  for  it  is 
better  to  find  the  bottom  of  the  sea  with  the  lead  than  with  the 
ship's  keel.  The  navigator  will  not  then  have  to  make  all  kinds  of 
explanations  before  a  l)oard  of  inquiry  as  to  how  it  happened. 


DIVISION  \. 

TlIK    TIDKS. 

The  tides  are  regulated  l)y  the  joint  attraction  or  combined 
action  of  the  snn  and  moon.  The  moon,  being  the  closer  to  the 
earth,  exerts  the  more  attractive  force,  while  the  sun,  although 
much  largei-.  doe^^■  not  exei't  so  nuicli  Unw  as  tlic  ninon,  being  so 
far  distant  from  the  earth.  That  particular  part  of  the  earth's 
surface  over  which  the  moon  is  vertical  has  the  largest  tides,  that 
part  of  the  earth's  surface  directly  opposite  having  the  smallest 
tides.  Large  tides  are  called  "spring  tides"  and  the  small  tides 
aie  called  "neap  tides."  The  sun  raises  a  smaller  tidal  wave  than 
tlie  moon,  hut  both,  if  jointly  acting  on  one  particular  part  of  the 
earth's  surface,  will  raise  higher  tides  than  the  moon  does  by  itself. 

We  have  several  methods  of  finding  the  time  of  high  water  at 
any  place,  one  being  the  Epitome  method  of  using  the  establish- 
ment of  the  port,  or  the  moon's  meridian  passage,  but  the  latter, 
although  theoretically  correct,  is  lial)le  to  be  very  much  in  error, 
owing  to  local  causes.  All  the  great  nations  of  the  earth  have  a 
regular  system  of  tide-oljservations  at  numerous  stations  scattered 
along  their  coasts,  where  instruments  register  the  tides.  The  in- 
strument so  nsed  is  called  a  "tide-gauge."  By  means  of  these 
automatic  observations  local  tide  conditions  are  found  and  pre- 
dicted for  future  use.  These  predictions  are  then  tabulated  for 
the  use  and  guidance  of  the  mariner.  But  even  these  tide-tables, 
although  prepared  with  extreme  care,  and  by  men  of  high  scientific 
attainments,  give  the  time  of  high  and  low  water  under  normal 
conditions,  but  the  time  of  actual  occurrence  may  be  somewhat 
different,  for  the  following  reasons : 

The  pressure  of  the  wind,  when  blowing  directly  into  a  harbor, 
forces  the  Avater  in,  in  the  case  of  a  flood-tide  making  it  run  much 
faster  than  it  would  under  ordinary  conditions,  thus  hanking  the 
water  up  in  the  harbor^  and  in  the  case  of  an  ebb-tide  retarding 
it  and  holding  it  back,  so  tliat  ine  eblj-tide  will  i-un  nnu-h  longer 
t!:'an  it  really  ought,  making  the  time  of  liigh  water  gi\-en  in  tlie 
tables  somewhat  in  error,  the  amount  depending  iipon  the  force  and 
direction  of  the  wind. 

Again,  supposing  there  have  been  very  heavy  rains  in  tlie  vicinity 
or  a  melting  of  snow  in  tlie  mountains.  Tn  s\ich  cases,  the  waters 
would  naturally  drain  into  the  valleys  and  rivers,  and  in  their  en- 
deavor to  reach  the  sea.  ri'tard  tlie  tlood-tide  with  tlu'ir  weiudit.  and 


248  Taylor's  Moderx  Xavigatiox. 

accelerate  the  ebb-tide,  and  at  the  same  time  cause  the  ebb-tide  to 
run  longer  than  the  time  tabulated.  Navigators,  understanding 
these  points,  must  use  the  tide-tables  with  caution,  for  the  amount 
of  rain  or  the  direction  of  the  wind  cannot  be  predicted  years  in 
advance.  If  they  could,  then  the  tables  might  be  so  computed  as 
to  take  into  consideration  these  conditions. 

A  knowledge  of  the  tides,  with  the  time  of  their  occurrence,  to- 
gether with  the  strength  of  currents,  is  very  necessary  to  the  navi- 
gator, especially  where  he  has  to  cross  shallow  bars  at  the  entrance 
to  ports. 

Bule  to  Find  the  Time  of  High  Water  hy  Means  of  the  American 
Tide-Tahles. 

Turn  up  Table  3,  which  contains  the  tidal  difference,  tidal  con- 
stants, and  the  standard  ports  for  reference,  etc.;  look  down  the 
left  hand  column  until  you  find  the  name  of  the  port  for  which  you 
wish  to  find  the  time  of  high  and  low  water,  and  when  found,  take 
the  name  of  the  standard  port  for  reference  directly  abreast  of  it, 
also  the  number  of  the  page  and  the  local  time  of  the  tidal  differ- 
ence for  high  and  low  water,  being  careful  to  note  the  signs  of  plus 
or  minus  which  are  prefixed  to  them;  next  turn  up  the  standard 
port  in  the  body  of  the  book,  and  under  the  month  and  abreast  of 
ihe  date  take  out  the  figures  which  stand  abreast ;  it  will  be  noticed 
here  that  there  are  two  lines  for  each  date,  the  top  line  giving  the 
times  of  the  tides  as  they  occur,  and  the  figures  which  stand  under 
these  times  giving  the  heights ;  mark  them  all  down  :  next  see  which 
is  the  high  and  which  the  low  water  by  noticing  the  figures  of  the 
heights  which  stand  under  the  times;  if  high  water,  the  height  will 
be  large,  and  if  low  water,  the  height  will  be  small;  having  now 
distinguished  which  is  high  and  which  is  low  water,  take  the  tidal 
differences  which  are  found  in  Table  3,  and  apply  them  according 
to  the  sign  of  plus  or  minus;  this  will  give  the  times  of  high  water 
and  of  low  water  for  that  date ;  if  the  hours  are  less  than  12,  it  is 
jnorning  time,  if  more,  it  is  afternoon,  and  when  reduced  by  12, 
will  give  time  in  the  afternoon. 

The  navigator  should  be  very  careful  to  read  the  explanation  at 
the  foot  of  each  page  in  regard  to  the  time,  as  the  time  at  ship 
may  differ  considerably  from  the  time  given  by  the  tables. 

Example. — March  16,  189G.  Acquired  the  times  of  high  and 
of  low  water  at  Cape  Clear,  Ireland. 


The  Tides.  -4'.) 


Look  in  the  index  at  vud  of  tables  for  Ii-eland  and  take  the  num- 
ber of  the  page,  which  is  410.  turn  up  page  410  and  search  for 
Cape  Clear,  under  Irehmd.  and  when  found  note  the  standard  port 
for  reference,  whicli  is  Queenstown.  page  288.  Differences  for 
time  H.W. — 0''  43™;  L.W. — 0"  56'".  Differences  for  heights, 
H.W.— 3^5;  L.W.— 0M5. 

Next  open  the  tables  at  page  288,  and  under  March,  abreast  of  the 
16th  day,  will  be  found: 

Times       0:0B     6:07       12:22     18:25  (hours  and  minutes). 

Heights     0.7     10.6  1.8       10.5     (feet  and  tenths). 

By  examining  the  heights  under  the  different  times,  it  will  >? 
seen  that  the  figures  under  6:07  and  18:25  are  greater  than  the 
others,  therefore  these  two  times  must  be  for  high  water  and  the 
others  for  low  water. 

L.^^^ 

Times  0:06 

Differences     0:56 

23:10 

11:10  p.m.    of  previous  day. 

The  first  time  given  by  table  being  0  :06,  and  the  low  water  dif- 
ference being  subtractive,  it  is  necessary  to  borrow  24  hours,  giving 
a  result  of  11'*  10"*  p.m.  of  preceding  day,  leaving  only  three  times 
of  tidal  occurrences  for  March  IGth. 

In  such  a  case  it  is  necessary  to  take  the  first  time  of  tide  for 
the  next  day,  viz.,  March  17th,  which  is  0:38,  and  subtract  the 
low- water  difference  and  if  the  difference  is  greater  than  the  tabu- 
lated time,  the  result  will  be  the  time  of  the  last  tidal  occurrence 
on  March  Ifith,  but  if  less,  there  will  be  no  other  for  that  day. 

h.  m. 
First  tide  on  March  17th.  0:38  Height.  0.1)  ft. 

L.W.  difference 


H.W. 

L.W. 

H.W. 

6:07 

12:22 

18:25 

0:43 

0:56 

0:43 

5:24  A.M. 
s  day. 

11:26  A.M. 

17:42 
5:42  P.M. 

h.  m. 
0:38 
-  0:56 

23:42 
16th  11:42  V 

Time  of  2d  L.W.  on  Marcli  16th  11:42  p.  m. 

Example.— Jaimarj  16.  1896.  Find  the  times  of  high  and  of 
low  water  at  Boston,  Massachusetts. 

By  searching  in  Table  3  of  the  Tide-tables  it  will  be  found  that 
Boston  is  a  standard  port  for  reference,  therefore  it  will  be  neces- 
sarv  to  take  only  the  numlier  of  the  page,  viz.,  ry2.  and  on  that 


250  Taylor's  :\[odern  Xavigation'. 

page,  under  Jaiuiary,  abreast  of  the  IGtli  day,  take  the  time  and 

heights  and  mark  tliem  down,  thns : 

Times     0:12     6:10     12:18  18:42     (hours  and  minutes). 
Heights  8.7       0.6       10.1      -.4       (feet  and  tenths). 

The  heights  under  t]ie  first  and  second  times  being  the  greater, 
tlie  times  above  them  must  therefore  be  the  high  water  and  the 
others  the  low  water. 

Exdmplc. — Find  the  times  of  higli  and  of  low  water  on  February 
1,  189(3,  for  Guaymas  harbor.  Gulf  of  California. 

By  reference  to  the  index  it  will  be  found  that  the  Gulf  of  Cali- 
fornia must  be  looked  for  on  page  362,  and  on  referring  to  this 
page  it  will  be  found  that  San  Diego  is  the  standard  port,  page 
120.  Time  difference,  H.W.  +2i>  'OS'^^ ;  L.W.  +2^^  lO'".  Height 
difEerence,  H.W.  +0^5;  L.W.  O'.!). 

Next  open  the  tables  at  page  120  and  find  San  Diego.  Then 
under  February,  and  abreast  of  the  1st  day,  take  the  times  and 
lieights,  and  mark  them  doAvn,  thus: 

Times     4:24     10:27     17:00     23:24   (hours  and  minutes). 
Heights  1.3         6.0     -0.7         5.2     (feet  and  tenths). 

It  Avill  now  be  seen  that  10 :27  and  23  :24  have  the  greatest  heights 
under  them,  therefore  they  are  the  times  of  high  water  and  the 
others  low  water. 


L.W. 

H.W. 

L.W. 

H.W. 

Times            4:24 

10:27 

17:00 

23:24 

Difference +  2:10 

+  2:02 

+   2:10 

+   2:02 

6:34  a.m.    12:29         19:10         25:26 

0:29  P.M.  7:10  p.m.  1:26  a.m.  of  next  date. 
The  times  of  high  aiul  of  low  water  at  Guaymas  wdll  therefore 
l)e,  L.W.  &"  34'"  A.M. ;  H.W.  0"  29'"  p.m.  ;  L.W.  1^  10'"  p.m.  But  the 
fourth  gives  the  time  of  high  water  at  1**  26"^  a.m.  of  next  day.  In 
such  case,  and  having  a  -f-  difference,  take  the  time  of  last  tide 
from  the  preceding  day  and  add  the  difference  to  it,  and  if  the 
i'csult  is  greater  than  24  hours,  reject  24.  The  result  will  be  the 
time  of  the  lirst  tidal  occurrence  on  tlie  required  day — in  this  case 
the  hist  tide  for  the  preceding  day,  viz.: 

h.  m. 
Last  tide  .lanuary  31st  22:50  Height,  5.1 

H.W.  difference  +   2:02 

24^2 
Time  of  the  first  H.W.  on  Feb.  1st  at  Guaymas  00:52  a.m. 


TiiK  Tides.  251 

HrLl'    TO    FiXl)   TIIK    ITkIOIIT  ok   TiDK    at   a    SlUOKDINATE   PORT. 

I^ntcr  'I'alilc  -"!  willi  the  name  of  lliu  port,  and  take  out  the  name 
of  the  standard  port  and  the  height  ditl'en'nee  for  l.oth  hi-'h  and 
J()\v  water,  noting  tht'  sign  of  -|-  or  — .  as  in  the  previous  r.xainplcs; 
luvxt  enter  Tal)le  1  with  the  name  of  the  staiuhird  port  and  the 
<hite;  take  the  heights  whicli  are  found  on  the  seeond  lini'  aiul  un- 
der the  time;  mark  these  heights  down  in  the  order  in  whicli  thev 
<;re  given;  then  apply  the  height  difference  from  Tahle  3,  according 
to  the  sign.  The  result  will  he  the  heights  of  the  tides  at  the  sub- 
ordinate port. 

The  foregoing  method  is  not  always  correct,  but  if  you  take  the 
ratio  of  the  range  found  in  the  right-hand  column  of  Table  3,  and 
multiply  each  predicted  height  by  it,  crossing  off  as  many  figures 
from  the  result  as  you  have  decimals,  the  final  result  will  be  the 
height,  very  much  nearer  than  in  the  first  rule. 

All  heights  found  will  be  reckoned  from  the  depth  of  water  given 
on  the  charts  of  that  particular  locality. 

Example.- — Find  the  times  and  heights  of  both  high  and  low 
water  at  Eed  Bluff,  Humbohft  Bay,  California,  on  January  18, 
189G.     Standard  Port,  Astoria,  page  128. 


H.W. 

L.W. 

Ratio  of  range, 

Tidal  diff.  -1"  3"'    - 

-1"  16- 

0.71 

Time 

3:23 

Height  8.2  ft.  H.W 

Tidal  diff. 

1:  3 

.71 

H.W. 

2:20  A.M. 

82 
574 

Height  5.822  ft. 

Time 

9:30 

Height  2.7  ft.  L.W. 

Tidal  diff. 

1:1(; 

.71 

L.W. 

8:14  A..M 

27 
189 

Height T9I 7  ft. 

Time 

14:58 

Height  7.6  ft.  H.W. 

Tidal  diff. 

1:  3 

.71 

13^  or 

76 

H.W. 

1:55  P.M. 

532 

5.396 

Time  L.W. 

21:16 

Height  0.5  ft.  L.W. 

Tidal  diff. 

1:16 

.71 

20:00  or 

Height  .355  or  0.4  ft. 

H.W. 

8:00  P.M. 

252  Taylok's  Modkux  Xa\iuatiox. 

The  above  is  au  example  of  the  correct  method  of  finding  the 
heights. 

The  following  is  the  doubtful  method  of  using  the  heights  given 
under  the  Tidal  Differences: 

The  height  differences  abreast  of  Red  Bluff,  Humboldt  Bay, 
California,  is  found  to  be  —2.2  feet  for  H.W.and  —0.3  feet  for 
L.W. 

Heights  for  jK-eceding  examiDle  for  January  18,  1896: 


8.2  ft.  H.W. 

2.7  ft.  L.W. 

Height  diff. 

-2.2 

Height  diff. 

-  .3 

Height 

6.0 

Height 

2.4 

7.6  ft.  H.W. 

0.5  ft.  L.W, 

Height  diff. 

-2.2 

Height  diff. 

-   .3 

Height 

5.4 

Height 

0.2 

By  comparing  the  results  of  this  last  method  with  the  first,  wo 
find  but  very  little  practical  difference;  but  as  this  is  not  always 
the  case,  it  is  advisable  for  the  navigator  to  use  the  first  method, 
remembering  always  that  the  heights  so  found  are  above  the  depths 
given  on  the  chart  of  the  locality,  with  the  exception  of  a  case 
when  the  height  difference  from  Table  3  is  minus  and  when  the 
height  taken  from  standard  port  is  also  minus.  In  this  case  the 
sum  of  the  two  must  be  taken  the  result  giving  an  amount  below 
the  figures  given  on  the  chart.  This  is  very  important  when  cross- 
ing shallow  bars  at  low  tide. 

TSE  OF  THE  TIDE-TABLES  WHEN"  TAKIXG  SOimDIN^GS 
WITH  THE  LEAD. 

There  is  a  lamentable  amount  of  carelessness  or  ignorance  in  re- 
gard to  the  proper  taking  of  soundings,  most  seamen  taking  the 
depth  as  found  by  the  lead  or  line  to  be  the  proper  depth,  and  there- 
fore referring  it  to  the  chart  without  taking  into  consideration  the 
amount  of  range  of  the  tide.  In  those  parts  of  the  world  where 
there  is  a  very  small  rise  or  fall,  it  does  not  matter,  but  where  there 
is  a  large  rise  or  fall,  it  is  plainly  to  be  seen  that  the  time  of  tide 
should  be  noticed. 

Recently  the  Hydrographic  Office  has  compiled  n  tal)h'  (Table 
2)  by  which,  with  a  little  practice,  the  navigator  may  (Ictcniiino  the 
exact  height  of  the  tide,  and  therefore  correct  the  soundings  taken 


The  TiuKS.  253 


by  the  lead  or  line  before  referring  it  to  the  chart.     This  method 
i-  of  the  utmost  importance  in  navigating  a  vessel  in  foggy  weather. 

Ride  1. — To  find  the  height  of  tlie  tide  at  any  tinu'  between  high 
and  low  water  at  a  standard  port. 

First  turn  up  in  Table  1  the  name  of  the  port;  then  with  the 
date  take  ont  the  times  and  heights,  and  mark  them  down  as  they 
read ;  then  with  the  time  at  which  yon  wish  to  find  the  height  of  the 
t'de  select  that  time  of  high  or  low  water  which  is  nearest  to  your 
own  time  and  take  the  difference,  being  careful  to  note  if  this  dif- 
ference of  time  is  before  or  after  the  time  found  in  Table  1 ;  next 
note  the  difference  of  the  heights  between  the  next  low  or  the  next 
high,  as  the  case  may  be;  this  you  will  call  the  range  of  tide;  now 
turn  up  Table  2  with  the  standard  port,  and  read  on  the  top  of  the 
page  to  see  if  it  is  high  or  low  water,  and  if  the  hours  are  before  or 
after  low  or  high  water.  Look  under  these  hours  and  abreast  of  the 
range  of  tide,  and  take  therefrom  the  correction,  to  be  applied  to 
the  preoicied  height  taken  from  Table  1,  to  be  added  to  a  L.W. 
height  and  subtracted  from  a  H.W.  height.  The  result  will  be 
the  height  of  the  tide  at  the  required  time. 

Huh  2. — If  it  is  required  to  find  the  height  of  the  tide  at  a 
subordinate  port,  proceed  by  the  following  rule:  Multiply  the 
value  taken  from  Table  2  by  the  ratio  of  the  range  taken  from 
Table  3.  The  result  will  be  the  correction,  to  be  applied  to  the 
predicted  tide  taken  from  Table  1. 

A.M.    on 
December  10,  1896,  at  Coos  Bay.  Oregon,  standard  port  Astoria  ? 

Time  diff.  H.W.— Qi^  4T'«;  L.W.  —0"  ST"".   Eatio  0.77. 

L.W. 

23:38  (hours  and  minutes). 
1.2     (feet  and  tenths). 

Time  nearest  to  given  time  5:26  11:44 

Tidal  diff.  -47  -51 

Time  1st  H.W.  4^  10:'53 

Given  time,  7:50  7:50 

Time  past  1st  H.W.   3^      Time  l)efore  1st  L.W.  3:03 


H.W. 

L.W. 

H.W. 

Times     5:26 

11:44 

17:08 

Heights  7.() 

2.9 

7.1 

254  Taylor's  Mouerx  Xavigatiox. 

It  will  be  noticed  that  the  1st  L.W.  is  a  little  nearer  to  the  given 
time  than  the  1st  H.W.,  therefore  we  will  take  it. 

2.9 

7.6 

The  difference  of  heights  between 


1st  L.W.,  and  1st  H.W.  ' 

We  will  next  nse  the  difference  for  the  range,  and  enter  Table  2. 
Then  under  3'^  before  L.W.,  in  the  section  marked  "Astoria." 
and  abreast  of  the  range  5  feet,  we  find  2.2  feet.  This  multiplied 
by  the  ratio  of 

0.77 
2.2 

1  694,  or  1.7  feet,  which  must  be  added  to  the  predicted  height, 

namely: 
2.9 

1.7,  to  be  added  to  the  depth  on  the  chart  of  the  locality,  or 
T^  subtracted  from  the  depth  found  by  the  lead  line. 


DIVISION  XI. 

THE  SEXTANT  AND  ITS  USES. 


The  sextant  is  an  instrument  of  precision  for  the  measuring  or 
angles  by  the  system  of  double-reflecticn. 

To  Select  a  Good  Sexiaiit. — A  purchaser  sh.ouki  first  know 
where  to  look  for  possible  defects,  which  should  be  done  in  the  fol- 
lowing manner: 

Eirst,  to  see  if  it  is  cut  correctly.  Place  the  t  on  the  vernier 
so  that  it  will  cut  exactly  with  any  line  or  cutting  on  the  arc.  Then 
search  along  to  the  last  cutting  of  tlie  vernier  and  see  if  that  lin? 
cuts  also.  If  it  does,  the  sextant  is  cut  correctly  at  that  particular 
part  of  the  arc.  The  purchaser  should  try  at  least  "20  different 
places  on  the  arc  before  final  selection.     If  tliere  is  any  one  portion 


25(\  Taylor's  ^[odeisx  Xavigatiox. 

oC  the  arc  where  these  lines  do  not  cut,  reject  the  instrument,  as  it 
will  give  a  wrong  reading  when  taking  an  observation. 

S  jcond,  to  see  if  the  sextant  is  in  perfect  plane.  Place  the  ver- 
nier at  about  4:0°.  Hold  the  instrument  with  the  face  up  and  the 
arc  from  you,  and  look  obliquely  into  the  index-glass  as  in  making 
Ihf  first  adjustment  and  see  if  the  true  and  reflected  arcs  appear 
in  one  continuous  line.  If  they  do,  the  glass  is  perpendicular  to 
that  particular  part  of  the  arc.  ]S'oiv  move  the  vernier  along  the 
arc  and  see  if  the  true  and  reflected  arcs  are  still  in  one  line.  If 
so,  the  sextant  is  in  plane;  but  if  }ou  see  the  true  and  reflected 
lines  higher  in  one  part  of  the  arc  and  lower  in  another  part,  then 
you  will  know  that  the  sextant  is  out  of  plane.  Reji?ct  the  sextant 
for  this  reason,  also,  as  you  will  have  a  different  index-error  on 
eveiy  part  of  the  are. 

Third,  to  see  if  the  index-bar  niovss  on  a  perfect  center.  This 
requires  a  keen  eyesight  and  a  little  practice.  Move  the  vernier  to 
the  right-hand  side  of  the  arc.  ]Si'ote  the  space  between  the  edge 
of  the  vernier  and  the  edge  of  the  graduated  arc  on  both  sides  of  the 
vernier.  Move  the  index-bar  now^  to  the  other  side  of  the  arc  and  see 
if  there  is  the  same  amount  of  space  between  the  edge  of  the  ver- 
nier and  the  edge  of  the  graduated  arc.  If  so,  then  it  is  in  center; 
but  if  not  in  center,  the  error  that  would  arise  from  this  defect 
would  be  in  the  reading  of  the  sextant,  as  the  lines  on  the  vernier 
will  be  diagonal  instead  of  in  a  straight  line  with  those  on  the  arc. 

Fourth,  to  see  if  the  vernier  fits  close  to  the  arc,  for  if  there  is  a 
space  between  them  and  the  sextant  should  be  held  a  little  side- 
ways, an  error  will  arise  in  the  reading.  This  can  easily  be  fixed, 
as  a  rule,  by  placing  a  new  spring  in  the  back  of  the  vernier. 

Color-Shades. — In  sextants  of  the  best  make  the  shade-glasses 
are  of  a  neutral  tint,  being  of  no  particular  color,  but  they  are  of 
different  degrees  of  density.  Errors  arise  in  observations  from 
having  common  glass  in  these  shades,  and  from  their  not  being 
properly  fitted  to  the  sextant.  Tests  of  tlie  shade-glasses  should 
be  made,  to  find  if  there  is  any  error,  by  measuring  known  angles 
with  the  glasses,  either  separately  or  in  pairs,  and  the  error  found 
is  to  be  used  in  correcting  altitudes  thereafter  when  the  glasses  are 
used. 

To  Illustrate  the  Effect  of  had  Shade-Glasses. — Supposing  you 
are  inside  of  a  room,  looking  through  the  window  at  some  station- 
ary object  in  the  street,  and  by  moving  your  head  a  little  one  way 
or  another,  the  ol)ject  becomes  distorted  out  of  its  proper  form. 


The  Sextant.  257 


This  is  caused  by  an  error  in  parallelism  in  the  glass.  The  same 
thing  occurs  with  the  color-shades  of  a  sextant. 

To  Handle  a  Sextant  Properly. — Lift  it  always  by  its  frame  or 
handle.  ISTever  take  hold  of  any  of  the  glasses,  as  by  so  doing  you 
may  disarrange  the  adjustments.  jSTever  put  your  thumb  or  fingers 
on  the  arc,  as  the  moisture  from  your  hand  will  tarnish  it,  and  if 
the  skin  on  your  thumb  or  finger  is  very  rough,  it  will  scratch  the 
arc  and  eventually  obliterate  the  divisions. 

To  Take  Care  of  a  Good  Sextant. — An  officer,  on  first  joining 
the  ship,  should  select  a  good  place  in  his  berth  for  a  shelf  whereon 
to  place  his  sextant  so  that  it  will  keep  dry  and  also  be  out  of  the 
Avay  and  still  be  handy.  Bore  two  holes  in  the  bottom  of  the  sex- 
tant-box and  screw  the  box  down  to  the  shelf  so  that  it  will  not 
move  when  the  ship  is  rolling.  It  is  not  necessary  to  carry  the 
sextant-box  on  deck  every  time  an  observation  is  taken.  If  there 
is  a  centerpiece  in  the  cover  of  the  box,  break  it  out,  as  it  is  only 
in  the  way  at  sea,  for  the  reason  that  if  an  observation  is  taken  and 
tlie  vernier  left  to  stand  as  it  is,  when  placing  the  sextant  in  the 
box  the  lid  will  not  close  unless  the  vernier  is  moved.  The  reason 
why  the  vernier  should  be  left  at  the  last  reading  is,  that  if,  after 
taking  an  observation  and  working  it  up,  something  did  not  come 
out  right,  the  sextant  may  be  again  scrutinized  to  see  if  it  had  been 
read  correctly.  After  taking  an  observation  in  damp  weather  the 
glasses  and  arc  should  be  wiped  very  carefully  with  a  piece  of 
chamois  leather  before  the  instrument  is  placed  in  the  box.  If  this 
is  not  done,  the  silvered  glasses  will  eventually  become  dull.  The 
sextant  should  never  be  left  exposed  to  a  hot  sun  for  any  length  of 
time. 

A  young  and  ambitious  navigator  in  possession  of  a  good  sextant 
should  refrain  from  continually  moving  the  adjusting-screws  be- 
cause the  instrument  happens  to  be  a  little  out.  By  so  doing  the 
screw  will  become  slack,  and  shaking  the  sextant  will  put  it  out  of 
adjustment.  Those  wishing  to  experiment  on  the  adjustments 
should  provide  themselves  Avith  a  cheap  instrument,  so  that  if  it 
should  be  broken  it  would  not  matter  very  much. 

If  the  screws  of  the  sextant  should  get  slack  they  may  be  stiffened 
up  by  taking  a  little  common  table-salt  and  wetting  it,  and  then 
with  a  match-stick  putting  some  of  this  wet  salt  around  the  base  of 
the  screws.  This  will  stiffen  them  so  hard  that  it  will  take  a  chip- 
ping-hammer  to  get  the  screws  out  again.  After  using  the  sextant 
do  not  lay  it  on  the  scuttle  or  on  the  deck  in  such  a  position  that  if 

Taylor's  Mod.  Xav.  17. 


258  Taylor's  Modern  Xavigatiox. 

the  ship  were  to  give  a  lurch  it  would  be  likely  to  take  a  journey 
into  the  lee  scuppers,  for  this  is  likely  to  injure  the  instrument. 

The  sextant-box  contains,  in  addition  to  the  sextant,  several  at- 
tachments, such  as  the  plane-tube,  which  has  no  glasses,  and  the 
short  telescope  and  the  inverting-telescope,  both  with  glasses.  Thesis 
telescopes,  when  used,  must  be  focused  properly  to  suit  the  eye  of 
the  observer.  When  looking  through  the  inverting-telescope,  things- 
appear  to  be  turned  upside  down.  It  will  be  noticed  also,  that  there 
are  four  wires  in  this  telescope,  two  of  them  being  at  right  angles 
with  the  other  two.  It  is  generally  considered  to  be  the  best  one  to 
be  used  when  taking  observations,  but  it  requires  a  little  practice. 
There  are  also  one  or  two  colored  caps  for  the  ends  of  the  telescopes, 
in  case  they  should  be  needed  for  use  when  the  sun  is  very  bright. 
A  small  lever  and  a  screw-driver  are  sometimes  supplied  for  moving 
the  screws  when  adjusting. 

We  will  now  proceed  to  name  the  different  parts  of  the  sextant, 
as  follows.     (See  figure.) 

A  to  A — Arc.  I — Horizon  shade  glasses. 

C — Tangent-screw.  J — Screws  in  2d  adjustment. 

D — Index-glass.  K     Screws  in  1st  adjustment. 

E — Horizon-glass.  L — Screws  in  3d  adjustment. 

F — Telescope.  M— Handle. 

G — Microscope.  N — Telescope-collar. 

H — Index  shade-glasses.  W — Vernier. 

To  Bead  the  Sextant. 

The  student,  in  the  first  place,  should  supply  himself  with  an  in- 
strument and  follow  out  the  instructions  herein  given,  and,  if  pos- 
sible, he  should  get  the  help  of  a  shipmate  who  has  some  knowledge 
of  the  subject. 

The  arcs  of  some  sextants  are  cut  to  20,  some  to  15,  and  some 
to  10,  the  latter  being  the  most  modern.  We  will  describe  here  only 
the  method  of  reading  a  sextant  cut  to  10,  that  of  reading  the  others 
being  almost  identical  with  it, 

A  sextant  cut  to  10  has  each  degree  divided  into  six  spaces,  each 
space  being  equal  to  10',  and  the  vernier  is  divided  into  10  equal 
parts,  each  long  stroke  being  1',  and  between  each  long  stroke  or 
minute  are  six  spaces,  each  space  being  equal  to  10"  of  arc.  It  is  not 
necessary  in  actual  practice  to  read  a  sextant  to  seconds,  the  nearest 
minute  always  being  sufficient,  except  when  taking  an  observation 
of  the  moon. 


The  Sextant.  259 


First  find  the  starting-point  of  the  arc,  which  is  marked  0, 
or  with  an  t-  Also  notice  the  starting-point  on  the  vernier,  which 
is  marked  similarly  to  the  arc.  Place  the  0  on  the  vernier  to  the  0 
on  the  arc,  making  the  lines  cut  exactly.  The  sextant  will  then 
stand  0.  Xow  move  the  vernier  by  means  of  the  tangent-screw 
nntil  the  0  of  the  vernier  is  in  a  direct  line  with  the  first  cutting  to 
the  left  of  the  0  on  the  arc.  The  sextant  will  then  stand  10'  of 
arc.  Xow  move  the  vernier  until  the  0  of  the  vernier  is  in  a  direct 
line  with  the  fourth  cut  to  the  left  of  the  0  on  the  arc.  The  sextant 
will  then  read  40'.  Now  move  the  vernier  again  by  means  of  the 
tangent-screw  until  the  0  of  the  vernier  is  in  a  direct  line  with  the 
first  cutting  to  the  left  of  the  first  long  line,  which  represents  a 
degree.  Then  the  sextant  will  stand  at  1°  10'.  This  method  gives 
the  reading  only  to  the  nearest  10'  of  arc. 

To  Read  the  Odd  Minutes. — Place  the  0  of  the  vernier  so  that 
it  will  cut  somewhere  between  1°  10'  and  1°  20'.  It  now  being 
past  1°  10',  search  along  the  vernier  until  you  find  one  of  the  strokes 
cutting  one  of  the  lines  on  the  -arc.  Supposing  that  the  6  on  the 
vernier  cut.  one  of  the  lines  on  the  arc,  you  would  add  this  6  to  the 
10',  making  1°  16'.  With  a  little  practice,  and  a  little  common 
sense,  the  student  will  now  be  able  to  read  a  sextant  cut  to  10. 

To  Read  off  the  Arc,  or,  as  it  is  Called,  the  Arc  of  Excess.— 0^ 
the  arc  is  that  part  to  the  right  of  the  0.  Place  the  0  of  the  vernier 
so  that  it  will  cut  with  the  first  cutting  to  the  right  of  the  0  on 
the  arc.  The  sextant  will  then  stand  at  10'  off  the  arc.  Now  place 
the  0  of  the  vernier  so  that  it  will  be  in  a  direct  line  with  the  second 
cutting  to  the  right  of  the  0.  The  sextant  will  then  stand  at  20' 
off  the  arc.  Now  suppose  that  the  0  of  the  vernier  comes  between 
the  second  and  third  cutting  to  the  right  of  the  0 ;  then  the  sextant 
would  read  20'  and  some  more.  So,  search  along  on  the  vernier  and 
see  which  line  cuts.  Suppose  that  the  4  were  to  cut ;  then  it  would 
count  as  6,  when  reading  from  the  left  to  the  right.  This  6  is  to 
be  added  to  the  20',  making  26'  off  the  arc,  Remember,  when  read- 
ing the  vernier  off  the  arc,  you  must  begin  at  the  left  and  read 
towards  the  right ;  therefore  9  would  be  1,  8  would  be  2,  and  so  on. 

Adjustments  of  the  Sextant. 

The  first  adjustment  is  to  see  that  the  index-glass  stands  perpen- 
dicular to  the  plane  of  the  instrument. 

To  Make  the  Adjusttnent.—ClumY)  the  sextant  at  about  40°  on 


260  Taylor's  Moderx  Xavigatiox. 

the  arc,  holding  the  instrument  with  the  face  up  and  with  the  arc 
from  you.  Look  obliquely  into  the  index-glass  and  see  if  the  true 
and  reflected  arcs  are  in  one  continuous  line,  one  part  being  neither 
higher  nor  lower  than  the  other.  If  so,  the  index-glass  is  perpen- 
dicular, but  if  not,  make  it  so  by  the  screws  in  the  frame  at  the 
back  of  the  glass. 

The  second  adjustment  is  to  see  if  the  horizon-glass  is  perpendic- 
ular to  the  plane  of  the  instrument. 

To  Make  the  Adjustment. — Clamp  the  0  of  the  vernier  to  the  0 
on  the  arc.  Hold  the  instrument  obliquely  and  look  through  the 
telescope  and  horizon-glass  at  horizon  and  see  if  the  true  horizon, 
which  is  seen  in  the  clear  part  of  the  glass,  and  the  reflected  hori- 
zon, which  is  seen  in  the  silvered  part  of  the  glass,  are  in  one  con- 
tinuous line ;  if  they  are,  then  the  horizon-glass  is  perpendicular  to 
the  plane  of  the  instrument ;  but  if  not,  then  make  it  so  by  the  screw 
found  at  the  back  of  the  glass. 

Different  sextants,  different  fashions  in  regard  to  the  position  of 
the  screws  used  in  the  second  and  third  adjustments,  but  you  must 
always  select  a  screw  that  will  throw  the  glass  forwards  or  back- 
wards in  the  second  adjustment. 


The  third  adjustment  is  to  see  if  the  index  and  horizon  glasses 
are  parallel  when  the  sextant  stands  at  zero. 

(The  word  "parallel"  meaning  that  if  an  imaginary  line  were 
drawn  across  the  face  of  the  index-glass  and  another  across  the  face 
of  the  horizon-glass,  the  lines  would  never  meet.) 

To  Make  the  Adjustment. — Clamp  the  sextant  to  0,  holding  the 
instrument  perfectly  upright,  as  when  taking  an  observation.  Look 
through  the  telescope  and  the  horizon-glass  at  the  horizon  and  see 
if  the  true  and  reflected  horizons  appear  in  one  continuous  line. 
If  they  do  so,  then  the  glasses  are  parallel,  but  if  they  do  not,  make 
them  do  so  by  the  screw  that  is  found  in  the  frame  at  the  back  of 
the  glass. 

In  selecting  the  screw,  choose  one  that  will  make  the  glass  turn 
as  if  on  a  pivot. 

The  fourth  adjustment  is  to  get  a  perfect  line  of  sight,  or.  as 
it  is  called,  the  line  of  coUimation.  This  line  of  sight  must  be 
parallel  to  the  plane  of  the  instrument. 


The  Sextant.  261 


To  Make  the  Adjustment. — Screw  in  the  inverting-telescopc 
Turn  round  the  eyepiece  until  two  of  the  wires  are  parallel  to  the 
plane  of  the  sextant.  Select  two  heavenly  bodies,  such  as  the  sun 
and  moon,  or  the  moon  and  a  star,  or  any  two  stars,  providing  they 
give  an  angle  of  at  least  i)0".  Direct  the  sight  to  the  body  to  the 
right  and  advance  the  vernier  along  the  arc  until  the  two  bodies 
appear  to  touch  each  other  nicely  on  the  wire  that  is  closest  to  the 
plane  of  the  sextant.  Then  dip  the  instrument  slightly  and  see 
if  they  touch  each  other  on  the  upper  wire.  If  they  do  so,  then 
the  line  of  sight  is  perfect,  but  if  not,  make  them  do  so  by  means 
of  the  two  small  screws  in  the  telescope-collar.  Cheap  sextants 
are  not  fitted  with  this  adjustment. 

We  will  now  proceed  to  find  the  index-error  of  the  sextant;  and 
the  young  navigator  is  again  cautioned  against  frequently  moving 
the  adjusting-screws.  If  there  should  be  a  small  error,  ascertain 
the  amount  and  apply  it.  The  result  will  be  the  same  as  if  the 
instrument  were  absolutely  correct. 

To  Find  the  Index-Error  hy  the  Horizon. — Clamp  the  sextant 
to  0.  Hold  the  instrument  perfectly  upright.  Look  through  the 
telescope  and  horizon-glass  at  the  horizon  and  see  if  the  true  and 
reflected  horizons  appear  in  one  line.  If  they  do  so,  there  is  no 
index-error;  if  they  do  not,  make  them  do  so  by  means  of  the 
tangent-screw.  The  reading  will  then  be  the  index-error,  to  be 
added  when  the  reading  is  off  the  arc  and  subtracted  when  on  the 
arc. 

To  Find  the  Index-Error  hy  the  Sun. — Screw  in  the  direct  tele- 
scope and  put  on  one  of  the  colored  caps.  Place  the  vernier  to 
twice  the  amount  of  the  sun's  semidiameter  on  the  arc,  which  is 
approximately  32'  of  arc.  Direct  your  sight  to  the  sun.  On  do- 
ing so  you  w^ill  see  two  suns  in  one  of  three  positions, — either 
touching  each  other  edge  to  edge,  overlapping  each  other,  or  sep- 
arate. In  any  case,  when  they  are  not  touching  each  other  edge  to 
edge  make  them  do  so  by  means  of  the  tangent-screw.  Eead  now 
what  is  on  ihe  arc,  and  mark  it  down  as  an  on-reading.  We  will 
suppose  that  this  reading  is  36'  40".  ISTow  place  the  vernier  to 
32'  off  the  arc,  and  direct  your  sight  to  the  sun  as  before,  and 
make  the  two  suns  touch  each  other  edge  to  edge,  and  read  what 
you  have  off  the  arc.  Mark  this  down  as  an  off-reading.  We  will 
suppose  that  this  reading  is  28'.  Subtract  the  smaller  from  the 
larger  reading  and  divide  the  remainder  by  2.     This  will  give  the 


2G2  Taylor's  Modern  Navigation. 


index-error  of  the  sextant,  to  be  added  if  the  greater  reading  is 
off  the  arc,  and  subtracted  if  the  greater  reading  is  on  the  arc.  In 
this  particular  case  the  index-error  will  be  4'  20",  to  be  sub- 
tracted. 

To  Prove  if  You  Have  Made  the  Ohservatiton  Correctly. — Add 
the  on  and  off  readings  together  and  divide  by  4.  The  result  will 
give  the  sun's  semidiameter  for  that  day ;  so,  turn  up  the  Almanac 
and  see  if  the  result  corresponds.  If  so,  you  will  assume  the  ob- 
servation to  have  been  taken  accurately  and  that  the  index-error  is 
therefore  correct. 

To  Measure  the  Altitude  of  the  Sun. — Slacken  the  clamp-screw 
so  that  the  vernier  will  move  freely.  Then  direct  your  sight  to 
that  part  of  the  horizon  directly  under  the  sun.  Move  the  vernier 
along  the  arc,  sweeping  the  horizon  a  little  at  the  same  time,  until 
you  catch  the  sun  in  the  horizon-glass,  then  make  the  lower  edge  of 
the  sun  touch  the  horizon  roughly.  Turn  the  sextant  over,  with  its 
face  up,  and  clamp  the  index.  Then  hold  the  sextant  in  the  first 
position  and  look  at  the  sun  again.  Make  the  contact  nicely  by 
means  of  the  tangent-screw.  It  is  generally  advisable,  when  taking 
an  observation,  to  give  the  sextant  a  vibratory  movement,  so  as  to 
make  the  sun  appear  to  sweep.  The  object  of  this  is  to  offset  any 
chance  of  not  holding  the  sextant  vertically,  for,  as  you  sweep,  the 
sun  must  always  pass  the  vertical  line,  and  the  lower  edge  of  the 
sun  must  never  be  below  the  horizon  when  sweeping,  but  must  just 
touch  it.  When  using  the  tangent-screw,  always  have  it  about  the 
middle  before  taking  an  observation,  so  that  it  will  have  plenty  of 
play.  There  has  been  many  a  screw  damaged  by  forcing  it;  in 
other  words,  the  worm  of  the  screw  has  been  broken.  This  method 
of  observing  the  sun  cannot  be  applied  to  a  star-observation,  as 
there  is  generally  more  than  one  star  visible  at  one  time,  and  you 
might  happen  to  get  the  wrong  star;  so  proceed  as  follows  in  ob- 
serving a  star : 

Place  the  vernier  at  0  and  direct  your  sight  to  the  star.  Advance 
the  vernier  along  the  arc,  and  the  star  will  then  appear  to  descend. 
When  on  or  near  the  horizon,  clamp  the  vernier  and  make  the  con- 
tact between  the  star  and  the  horizon  witli  the  tangent-screw. 

LEAD-LINE. 

The  lead-line  may  be  likened  to  a  blind  man's  stick,  for  it  is  to 
be  used  mostly  when  the  navigator  cannot  see  anything.  As  a 
blind  man  feels  his  way  along  the  street,  by  touching  objects  with 


The  Sextant.  2G3 


his  stick  that  he  recognizes  by  the  feel,  so  does  the  navigator,  as 
he  proceeds  iu  a  fog,  endeavor  to  touch  the  bottom  of  the  sea,  by 
the  use  of  the  lead-line,  bringing  up  the  nature  of  the  bottom  by 
the  arming  on  the  lead,  the  depth  of  water  being  indicated  by  the 
length  of  line  used. 

Many  serious  marine  disasters  might  have  been  averted  if  more 
attention  had  been  paid  to  the  lead-line.  It  is  better  by  far  to 
find  the  bottom  of  the  sea  with  the  lead-line,  than  with  the  bottom 
of  the  ship.  The  master  will  not  have  to  make  so  many  excuses 
wlien  before  the  inspectors,  explaining  mysterious  currents  and 
error  of  his  compasses,  if  he  pays  strict  attention  to  the  lead-line 
and  thus  prevents  his  vessel  from  going  ashore. 

The  Hand-Lead. 

1  fathom Deep   (no  mark) 

2  fathoms Leather  with  two  ends 

3  fathoms Leather  with  three  ends 

4  fathoms Deep    (no  mark) 

5  fathoms White  rag 

6  fathoms Deep  (no  mark) 

7  fathoms Red  rag 

8  fathoms Deep  (no  mark) 

\)  fathoms Deep  (no  mark) 

10  fathoms Leather  with  hole  in  it 

11  fathoms Deep  (no  mark) 

12  fathoms Deep    (no  mark) 

13  fathoms  Blue  rag 

14  fathoms Deep  (no  mark) 

15  fathoms White  rag 

16  fathoms Deep   (no  mark) 

17  fathoms Red  rag 

18  fathoms Deep    (no  mark) 

19  fathoms Deep   (no  mark) 

20  fathoms Two  knots,  or  leather  with  two  holes  in  it 

The  Deep-Sea  Line. 

25  fathoms One  knot 

30  fathoms  Three  knots 

35  fathoms   One  knot 

40  fathoms Four  knots 


26-i  Taylor's  Modern  Navigation. 

For  five  fathoms,  only  one  knot,  and  for  every  additional  ten 
fathoms,  one  more  knot.  The  length  of  an  ordinary  deep-sea  lead- 
line is  about  120  fathoms  or  more. 

The  above  rule  to  mark  the  lead-line  is  used  on  merchant  vessels, 
but  the  United  States  navy  places  at  13  the  same  mark  as  at  three 
fathoms. 

To  Cast  the  Deep-Sea  Lead  from  a  Sailing-Ship. 

Bring  the  ship  to  the  wind  and  back  the  main  yard.  Pass  the 
line  from  aft  forward  on  the  weather  side  clear  of  all,  bend  the 
lead  on  and  arm  it.  Station  about  half  a  dozen  men  along  the 
weather  rail,  and  let  each  man  take  from  5  to  10  fathoms  of  the 
line  in  his  hands.  When  all  is  ready  the  man  on  the  fore  part  of 
the  ship  heaves  the  lead  overboard,  at  the  same  time  calling  out 
the  words,  "Watch  there,  watch !"  each  man  repeating  these  words 
as  the  line  leaves  his  hands.  The  officer  stationed  in  the  after 
part  of  the  ship  then  takes  the  soundings.  The  arming  of  the  lead 
is  composed  of  tallow  or  soap,  and  is  placed  in  a  cavity  at  the  bot- 
tom of  the  lead  for  the  purpose  of  bringing  up  specimens  showing 
the  nature  of  the  bottom. 

To  Cast  the  Lead  from  a  Steamship. 

Stop  the  ship  and  heave  the  lead  the  same  as  on  a  sailing-ship. 

The  foregoing  rules  are  for  the  use  of  the  common  lead,  but 
there  are  in  use  at  the  present  date  numerous  sounding-machines 
or  apparatus.  Most  of  them  are  attached  to  the  common  lead-line, 
necessitating  the  stoppage  of  the  vessel  every  time  that  a  cast  is 
taken.  There  is  one  special  sounding-machine,  called  the  "Thom- 
son" apparatus,  by  which  can  be  found  the  depth  of  the  water  and 
the  nature  of  the  bottom  as  the  ship  moves  along  on  her  course,  no 
matter  at  what  rate  of  speed.  The  great  benefit  derived  by  using 
this  machine  will  be  readily  understood,  for  in  continually  stop- 
ping the  vessel  time  is  lost,  and  at  the  same  time  the  ship  is  car- 
ried along  by  the  current,  whereas  by  the  use  of  this  machine  it  is 
not  necessary  to  stop  the  ship,  and  it  is  therefore  easier  for  the 
navigator  to  keep  track  of  her.  Almost  all  vessels  of  any  size 
have  one  of  these  machines  on  board,  secured  to  the  after  part  of 
the  deck  for  use  at  any  time. 


The  Sextant.  265 


A  handbook  with  directions  for  use  is  given  with  the  machine, 
but  sometimes  this  description  is  mislaid  or  lost,  so  it  may  not  be 
amiss  to  describe  here  the  manner  of  its  use. 

The  box  is  firmly  secured  on  the  deck.  In  this  box  will  be  found 
a  wheel,  with  a  very  long  and  fine  steel  wire  wound  on  it.  When 
not  in  use,  this  box  is  filled  with  lime-water  covering  the  wheel  and 
wire  to  prevent  them  from  rusting.  When  about  to  use  it,  lift 
the  wheel  up  and  secure  it  to  the  top  of  the  box.  Take  the  end  of 
the  wire  and  make  it  fast  to  the  lead.  About  two  feet  above  the 
lead  seize  on  the  brass  tube  with  the  screw-cap  up  and  the  end  with 
the  small  hole  in  it  down.  Place  in  this  brass  tube  one  of  the  red 
glass  tubes  that  are  supplied  with  the  apparatus,  with  the  open  end 
down,  screwing  the  brass  cap  on  afterwards.  Now  hang  the  lead 
and  the  tube  over  the  stern,  with  the  wire  leading  over  the  small 
reel  on  the  taffrail,  keeping  the  brake  on  the  sounding-machine 
while  doing  so.  The  apparatus  is  now  ready  for  use.  Station  a 
careful  quartermaster  at  the  brake,  with  instructions  always  to 
keep  a  small  strain  on  the  wire  when  it  is  running  out.  The  offi- 
cer, standing  close  to  the  wire  and  holding  a  hook  pressing  gently 
on  the  wire,  will  give  the  order  to  "let  go."  As  soon  as  the  officer 
feels  the  line  giving  to  the  pressure  of  the  hook  which  he  holds  in 
his  hands,  he  must  call  out  sharply,  "stop."  The  man  at  the  brake 
will  then  stop  the  line  from  running  out  by  quickly  closing  the 
brake  down  hard. 

The  officer  and  his  assistant  must  act  smartly,  for  if  the  line  is 
allowed  to  run  out  slack,  it  will  kink  and  then  break. 

When  the  lead  has  reached  the  bottom,  ship  the  handles  to  the 
machine  and  wind  in  the  wire  until  the  lead  is  up  to  the  rail.  Then 
the  officer  will  open  the  brass  tube  and  take  out  the  glass  tube. 
Lay  this  glass  tube  in  the  boxwood  scale  that  is  supplied  with  the 
machine,  and  see  how  far  the  red  part  of  the  tube  comes  down  to 
the  scales.  This  will  indicate  the  number  of  fathoms.  Examine 
the  arming  of  the  lead  and  see  if  it  has  brought  up  the  nature  of  the 
bottom.  You  will  now  have  the  depth  of  the  water  and  the  nature 
of  the  bottom,  altliough  the  ship  was  going  at  full  speed. 

One  cast  of  the  lead  is  almost  as  useless  as  none  at  all,  for  it 
would  give  only  the  depth  of  the  water  in  that  particular  place,  but 
would  not  give  the  position  of  the  ship,  owing  to  the  unevenncss  of 


266  Taylor's  Modern  Xavigation. 

the  bottom  of  the  sea.  When  navigating  a  vessel  in  a  fog  along 
the  coast,  soundings  should  be  taken  at  regular  intervals,  in  fact 
every  half-hour,  especially  when  the  vessel  is  in  close  proximity  to 
the  land. 

After  each  cast  the  arming  of  the  lead  should  be  carefully  re- 
moved by  the  officer  in  charge  and  placed  on  a  slip  of  paper  with 
the  time  of  taking  the  cast,  the  depth  of  the  water,  and  the  distance 
run  by  the  log.  This  should  be  laid  upon  the  chart-room  table  for 
reference.  The  position  found  by  the  depth  of  w^ater  and  nature 
of  the  bottom  must  be  marked  on  the  chart  as  soon  as  found.  When 
all  the  positions  are  connected,  it  will  indicate  the  direction  in 
which  the  vessel  is  traveling,  and  the  navigator  can  act  accordingly, 
proceeding  with  caution. 


THE  LOG  AND  LOG-GLASS. 

There  is  a  strong  impression  among  seamen  at  the  present  day 
that  the  old-fashioned  or  common  log-line  is  out  of  date.  We  will 
explain  here  why  it  is  not  out  of  date,  so  that  the  wrong  impression 
may  be  done  away  with  as  soon  as  possible. 

The  common  log  gives  only  the  speed  of  the  vessel  at  the  time  of 
heaving  the  log,  so  it  should  be  heaved  at  least  every  hour,  to  get 
a  good  average  speed  of  the  ship,  because  vessels  do  not,  for  several 
reasons,  travel  at  a  uniform  rate  of  speed,  unless  it  be  a  steamship 
in  smooth  water.  Even  then  the  speed  found  would  be  the  rate  the 
vessel  is  traveling  through  the  water  and  not  over  ground.  Still, 
the  old-fashioned  log  is  the  one  upon  which  to  place  the  most  re- 
liance, as  it  does  not  get  out  of  order,  the  same  as  a  patent  log.  Be 
careful  in  regard  to  measuring  the  log-line  correctly  according  to 
the  glass  used,  and  to  test  it  frequently  by  remeasuring.  Also  test 
the  log-glass  frequently  by  comparing  it  with  the  second  hand  of 
the  chronometer. 

In  regard  to  the  patent  log,  note  the  following: 

The  harpoon  or  taffrail  logs  have  a  metal  rotator  of  a  fish-like 
form,  with  blades  or  fins  attached  at  a  certain  angle,  which,  by 
being  dragged  through  the  water,  revolves  a  certain  number  of 
times  in  a  nautical  mile,  the  number  of  revolutions  made  being 
registered  on  a  dial  indicating  the  number  of  miles.  If  this  log 
were  not  subject  to  get  out  of  gear,  it  would  give  a  prettv  accurate 
dislnncc  traveled  hv  the  slii|)  tlirough  the  water;  but  seaweed  mav 


The  Log. 


foul  this  rotator  and  prevent  it  from  revolving  in  the  water;  a 
hungry  shark  may  take  it  for  an  appetizing  bait,  and,  snapping  at 
it,  may  knock  the  blades  out  of  proper  angle ;  or  a  careless  quarter- 
master, sent  to  haul  the  log  in,  may  knock  it  against  the  stern  of 
the  ship,  and  thus  also  damage  the  rotator. 

The  inner  works  of  the  patent  log  are  simply  a  system  of  cog- 
wheels, something  like  the  works  of  a  watch.  These  cog-wheels  are 
liable  to  become  worn  or  get  dirty,  making  the  log  appear  to  run 
fast  or  slow,  just  as  an  ordinary  watch  when  not  kept  in  good  con- 
dition. Again,  if  the  ship  is  running  head  on  to  a  sea  with  a  patent 
log  out,  the  send  of  the  sea,  being  in  an  opposite  direction  from  the 
ship's  course,  will  cause  the  log  to  register  more  than  the  ship 
actually  travels,  and  the  amount  is  very  hard  to  determine.  If  the 
sea  is  following  the  ship,  it  will  send  the  rotator  after  her,  causing 
the  log  in  this  case  to  register  less  than  the  ship  actually  travels, 
but  how  much  can  not  be  determined,  as  it  depends  upon  the 
strength  of  the  sea. 

These  various  explanations  should  do  away  with  the  implicit  re- 
liance that  some  navigators  place  on  a  patent  log.  They  are  useful 
instruments,  'tis  true,  but  should  be  used  with  extreme  caution,  for 
many  vessels  have  been  lost  through  too  much  confidence  in  them. 

To  Test  a  Patent  Log  to  See  if  It  Registers  Correcthj. 

Select  some  fine  calm  day,  and  some  part  of  the  coast  where  there 
is  no  current.  When  off  a  certain  point  of  land  put  the  log  out  and 
note  what  is  registered  on  it.  Then  run  in  a  straight  line  for  some 
other  point,  and  again  note  what  is  registered  on  the  log.  This 
will  give  the  log  distance,  and  by  referring  to  a  chart  you  will  find 
the  correct  distance  between  the  points.  The  difference  between  the 
two  distances  will  give  the  amount  that  the  patent  log  is  fast  or 
slow.  This  error  must  be  used  as  a  rate  to  correct  distances  run  by 
the  log  in  the  future,  provided  that  it  does  not  get  out  of  gear,  but 
the  navigator  should  be  careful  to  test  the  log  whenever  an  oppor- 
iunity  occurs. 

The  writer  has  seen  as  many  as  three  patent  logs  in  use  at  one 
time,  one  over  the  stern  and  one  on  each  side,  towed  from  booms 
Tigged  out  abreast  of  the  foremast  and  each  one  of  the  logs  indi- 
cated a  different  distance  run,  but  regularly  every  half-hour  the 
junior  officer  of  the  watch  was  ordered  to  heave  the  log,  just  the 
■same  as  if  there  were  no  such  thing  as  a  patent  log  in  the  world. 

This  was  done  on  one  of  the  fast  Atlantic  liners. 


268  Taylor's  Modern  Navigatiox. 


Short  and  Handy  Rnh  to  Measure  the  Log-Line. 

This  method  is  safe  and  handy.  We  consider  here  that  there  are 
G,000  feet  in  a  nautical  mile  instead  of  6,080,  therefore,  to  the  mnn- 
ber  of  seconds  run  by  the  glass  annex  a  0  and  divide  by  6.  The  re- 
sult will  be  the  number  of  feet.  Then  double  the  remainder.  This 
will  give  the  odd  inches,  or  the  feet  and  inches,  to  be  measured  on 
the  log-line  for  one  knot.    Thus : 

6)28^0     4X2 

46  feet  8  inches 

It  will  be  noticed  by  this  rule  that  there  is  a  difference  between 
it  and  the  longer  and  more  correct  method,  amounting  to  several 
inches,  but  it  is  always  safe  to  assume  the  vessel  to  be  going  faster 
than  she  really  is,  which  is  the  case  here  by  assuming  a  knot  to  be 
46  feet  8  inches  instead  of  47  feet  3  inches.  The  knot  being  shorter, 
the  vessel  will  appear  to  be  traveling  faster  than  she  really  is,  and 
you  would,  therefore,  be  looking  out  for  danger  ahead  of  time. 

To  Marl:  the  Log-Line. 

After  determining  the  length  of  a  knot  according  to  the  glass 
used,  measure  it  on  the  deck,  at  some  convenient  place,  and  mark 
the  deck  with  a  few  copper  tacks  so  that  the  line  may  be  checked 
whenever  necessary,  without  calculating  it  all  over  again  and  hunt- 
ing the  ship  high  and  low  to  find  a  two-foot  ruler  or  tape-line  when 
in  a  hurry. 

Measure  the  required  length  from  the  white  rag  and  place  a 
piece  of  marlin  in  the  lay  of  the  line,  with  one  knot  on  it;  then 
measure  the  same  length  from  one  knot  and  place  a  mark  with  two 
knots;  then  again  measure  and  mark  3,  and  so  on  until  you  have  a 
sufficient  number  marked  on  the  line  according  to  the  greatest  speed 
the  ship  can  make. 

The  above  method  of  marking  a  log-lino  will  be  for  a  vessel  not 
traveling  at  a  greater  speed  than  10  or  12  knots  an  hour,  but  if 
she  is  a  fast  vessel,  say  a  20-"knotter,"  we  must  use  another  method, 
as,  the  bunches  of  knots  being  so  large,  the  line  is  likely  to  foul 
when  running  out.    In  such  a  case  use  the  following  method : 

Mark  the  log-line  similarly  to  the  Icad-line,  namely,  at  5  knots 
and  15  knots;  place  a  white  rag  of  common  calico  to  distinguish 


The  Log.  269 


it  from  the  stray-line  mark,  which  is  of  canvas,  at  7  and  17  knots 
red  flannel,  10  knots  leather  with  hole  in  it,  13  knots  blue  bunting, 
the  intermediate  mark  being  knots.  This  method  will  do  away  with 
the  big  bunches  of  knots,  and  is  the  one  used  on  board  of  large, 
speedy  ships. 


THE  LOG-LINE.  ^ 

Stretch  the  line  well,  and  at  about  12  or  20  fathoms  from  the  end 
put  a  white  rag  in  the  strands  of  the  line. 

The  amount  of  stray-line  depends  on  the  size  of  the  ship.  For 
a  ship  of  about  2000  tons,  allow  20  fathoms  ;  for  a  vessel  of  600 
tons,  allow  12  fathoms;  but  never  less  than  12  fathoms,  even  if  the 
vessel  is  smaller. 

Rule  to  find  the  Length  of  a  Knot. 

Multiply  the  number  of  feet  in  a  nautical  mile  (6080  feet)  by 
the  number  of  seconds  the  glass  runs  and  divide  by  the  number  of 
seconds  in  an  hour  (3600  sec). 

Exainidr. — What  is  the  length  of  a  knot  for  a  14-second  glass? 

3600.  14  sec.         6080  feet. 
14 


24320 
6080 


3600)85120(23  feet. 
7200 


13120 
10800 


2820 

12   (Multiplied  by  12  because  there  are  12 

3600)2"7840(7.7  inches.         ^"^^^^  "^  '^  ^o"^-) 
25200 


26400 
25200 


Answer. — 23  feet  7  inches  7  tenths. 


270  Taylor's  Modern  Navigatiox. 

What  is  the  length  of  a  knot  for  a  2-i-second  glass 

3600.     24  sec.  6080  feet. 

24 

.T432O 
12160 


3600)145920(40  feet. 
14400 


1920 
12 


3600)23040(6  inches. 
21600 


Answer. — 40  feet  6  inches. 


What  is  the  length  of  a  knot  for  a  28-second  glass? 

3600.     28  sec.  6080  feet. 

28 

48640 
12160 

3600)170240(47  feet. 
14400 

26240 
25200 


1040 
12 


3600)12480(3  inches 
10800 


Answer. — 47  feet  3  inches. 


Definitions 


271 


DEFINITIONS. 

In  most  books  on  navigation,  definitions  of  the  terms  used  are 
given,  but  here  they  will  be  given  in  such  a  manner  as  to  be  evident 
even  to  people  that  have  had  little  or  no  education,  thus : 

Q.  1 — What  is  a  great  circle? 

It  is  a  circle  whose  plane  passes  through  the  center  of  any  sphere. 

Note— A  great  circle  is  one  that  would  divide  the  earth  into 
two  equal  parts.  Supposing,  therefore,  that  an  orange  was  cut  into 
two  equal  parts,  the  flat  part  of  each  half  of  the  orange  would 
represent  the  plane.  When  again  joined  together  the  cut  would 
represent  a  great  circle.  See  Fig.  1.  P  C  P  or  E  C  E  would  be 
great  circles. 

Q.  2— What  is  the  vertex  of  a  great  circle? 

That  point  of  the  great  circle  which  has  the  greatest  latitude. 
In  all  srcat  circles  there  are  two  vertices,— one  in  the  Northern 


272 


Taylor's  Modern  I^avigation, 


and  one  in  the  Southern  Hemisphere.  See  Fig.  1.  M  E  and  M  E 
would  represent  the  vertices  of  the  great  circle,    M  E,  C,  M  E. 

Q.  3 — What  are  vertical  circles? 

Circles  whose  planes  pass  through  the  zenith  and  nadir  and  cut 
the  horizon  at  right  angles.  See  Fig.  2.  C,  observer;  X,  horizon; 
Z.  zenith;  JST,  nadir;  Z  X  N,  vertical  circle. 


Fig.  2 


VERTICAL  CIRCLES 

Z 


Q.  4 — What  is  a  right  angle? 

A  right  angle  is  formed  by  the  inclination  of  two  lines  which  are 
perpendicular  to  each  other  and  form  an  angle  of  90°.  Thus:  A 
North-and-South  line  as  indicated  on  the  compass  will  be  at  a 
right  angle  to  an  East-and-West  line.  See  Fig.  3.  X  C,  right 
angles  to  C  E ;  or  W  C  is  right  angle  to  S  C. 

Fi§.3 

RIGHT  ANGLES 
N 


Definitions.  273 


Q.  5 — What  is  an  oblique  angle  ? 

Any  angle  which  is  not  a  right  angle.     See  Figs.  4  and  5. 

Q.  6 — What  is  an  obtuse  angle? 

Any  angle  which  is  greater  than  a  right  angle.  Thus:  A  line 
drawn  from  the  center  of  a  compass  towards  the  East  and  another 
drawn  from  the  center  towards  N  X  W  will  give  an  obtuse  angle. 
See  Fig.  5. 

fig.  5 

Fig.  4  OBTU5E   OR  OBLIQUE 

ACUTE  OR  OBLIQUE 


Q.  T — What  is  a  spherical  angle? 

An  angle  drawn  on  the  surface  of  a  sphere  or  globe  contained 
between  two  great  circles  at  their  point  of  intersection.  See  Fig. 
1.    B,  M  E,  P,  spherical  angle. 

Q.  8 — What  is  meant  by  an  arc  ? 

An  arc  is  any  part  of  the  circumference  of  a  circle. 

Note.— The  difference  between  N.  20°  E.  and  N.  30°  E.  will  give 
10°  of  arc.     See  Compass. 

Q.    9 — What  is  the  complement  of  an  angle  ? 

An  angle  which  added  to  another  would  make  an  angle  of  90°. 

Q.  10 — -What  is  the  supplement  of  an  angle? 

An  angle  which  added  to  another  would  make  an  angle  of  180°. 

Q.  11 — What  is  meant  by  the  equator? 

A  great  circle  around  the  earth,  midway  between  the  two  Poles. 
The  equator  is  90°  from  either  Pole.    See  Fig.  1.    E  C  E,  equator. 

Q.  12— What  are  the  Poles? 

The  ends  of  the  axis  of  the  earth,  around  which  the  earth  re- 
volves. 

Note. — Supposing  you  were  to  take  a  perfectly  round  ball  and 
thrust  a  stick  through  the  center  of  it.  This  stick  would  represent 
the  axis,  and  that  part  of  it  which  protrudes  through  the  ball 
would  represent  the  Poles  of  that  particular  sphere  or  ball.  See 
Fig.  1.    P  C  P,  axis;  P  P,  Poles. 

Q.  13 — What  are  true  meridians? 

True  meridians  are  great  circles  passing  from  both  true  Poles, 

Taylor's   Mod.   Nav.   IS. 


274 


Taylor's  Modern  Navigation. 


and  cut  the  equator  at  right  angles.  See  Fig.  1.  All  circles 
passing  from  P  to  P  are  true  meridians. 

Q.  14— What  is  longitude? 

Longitude  is  an  arc  of  the  equator  between  the  meridian  of 
Greenwich  and  the  meridian  which  passes  through  the  place.  That 
part  of  the  world  which  is  on  the  East  side  of  the  meridian  of 
Greenwich  is  termed  East  longitude,  and  that  on  the  West  side. 
West  longitude.  See  Fig.  1.  P  C,  meridian  of  Greenwich;  P 
a,  meridian  of  place ;  C  a,  longitude. 

Q.  15 — What  is  difference  of  longitude? 

Difference  of  longitude  is  an  arc  of  the  earth's  equator  between 
the  meridians  which  pass  through  any  two  places.  See  Fig.  1. 
P  X  G,  meridian  of  one  place;  P  X  H,  meridian  of  another; 
G  H,  diff.  of  longitude. 


Fig.  6 


DIP 

2 


c  1  _^ 


Q.  16— What  is  departure? 

Departure  is  the  -distance  in  nautical  miles  a  ship  sails  true  East 
or  true  West;  departure  meaning,  in  reality,  the  number  of  miles 
a  ship  has  departed  from  the  true  Xorth  or  South  line  passing 
through  the  place  the  ship  was  in  originally.  See  Fig.  8.  D  P, 
departure. 

Q.  17 — What  is  a  prime  meridian  ? 

A  prime  meridian  is  the  fixed  meridian  from  which  we  reckon 
our  longitude.  In  navigation  we  use  the  meridian  of  Greenwich. 
Some  countries  have  tried  to  introduce,  at  different  times,  another 
meridian  as  the  prime,  but  the  confusion  following  such  an  attempt 


Definitions.  275 


proved  to  them  very  clearly  that  it  would  be  more  convenient  if  all 
seamen  reckoned  from  the  same  meridian;  therefore  all  countries 
hfive  adopted  the  meridian  of  Greenwich  as  the  starting-point  from 
which  to  reckon  longitude.    Sec  Fig.  1.    P  C,  prime  meridian. 

Q.  18 — What  is  meant  by  the  first  point  of  Aries? 

The  point  where  the  sun  crosses  the  equator  passing  from  South 
to  North  declination.  The  point  where  the  sun  crosses  the  equator 
passing  from  North  to  South  is  called  the  point  of  Libra. 


Fig.  7 


\ 


Son 

O 


Artificial  Horizon 


Q.  19 — What  is  the  prime  vertical? 

A  vertical  circle  passing  through  the  zenith  and  the  East  and 
W^est  points  of  the  horizon.  Any  body  on  this  circle  must  bear  true 
East  or  West.  See  Fig.  1.  C,  observer;  P,  zenith;  looking  North 
or  South,  E  P  E,  prime  vertical. 

Q.  20 — What  is  the  ecliptic? 

The  ecliptic  is  the  great  circle  that  the  sun  appears  to  describe 
in  a  year.  It  is  the  earth's  real  path,  as  the  sun  does  not  move,  but 
the  earth  itself  revolves  around  the  sun. 

Q.  21— What  are  the  tropics  ? 

The  tropics  are  two  small  circles  round  the  earth,  parallel  to  the 
equator,  limited  by  the  amount  of  the  sun's  declination,  which  is 
231/2°  on  either  side  of  the  equator.  The  North  tropic  is  called 
the  Tropic  of  Cancer,  and  the  Southern  one  the  Tropic  of  Capri- 
corn.    See  Fig.  1.    T  T,  Tropic  of  Cancer;  t  t,  Tropic  of  Capri- 


276 


Taylor  s  Modern  Navigation. 


Q.  22 — What  is  the  equinoctial,  or  celestial  equator? 

The  equinoctial  is  the  earth's  equator  extended  to  the  sky,  or 
celestial  concave.  Thus,  supposing  it  were  possible  to  draw  a  line 
on  the  sky  itself,  which  should  coincide  exactly  with  the  equator  of 
this  earth.  Such  a  line  drawn  on  the  sky  would  be  termed  the 
celestial  equator,  or  the  equinoctial. 

Q.  23 — What  is  the  visible  horizon  ? 

The  visible  horizon  is  the  circle  which  bounds  the  view  at  sea, 
or  in  other  words,  where  the  sky  and  sea  seem  to  meet.  See  Fig.  (i. 
0,  observer;  H,  visible  horizon. 

Q.  24 — What  is  the  sensible  horizon  ? 

A  horizontal  plane  passing  through  the  place  where  the  observer 
is  standing.     Thus,   imagine   a   straight   line   drawn   from   Avhere 


Fig.  6  -  departure:,  etc 


Departure 


you  stand  and  extending  to  the  sky  and  being  at  a  right 
angle  to  a  plumb-line.  A  plumb-line  is  obtained  by  taking  a  piece 
of  string  and  tying  a  weight  on  the  end  of  it.  When  suspended 
freely,  this  line  would  hang  vertically.  See  Fig.  6.  0  S,  sensible 
horizon. 

Q.  25 — What  is  meant  by  the  rational  horizon? 

A  great  circle  whose  plane  passes  through  the  center  of  the  earth 
and  which  is  parallel  to  the  sensible  horizon.  Remember  that  a 
plane  is  a  flat  surface,  as  explained  in  one  of  the  preceding  defini- 
tions.   See  Fjg.  G.    C  R.  rational  horizon. 


Definitions. 


277 


Q.  26— What  is  nii  amplitude? 

It  is  an  arc  of  the  horizon  between  the  prime  vertical  circle  and 
the  object  observed  at  rising  or  setting.  It  is  reckoned  from  the 
East  at  rising  and  from  the  West  at  setting.  See  Fig.  9,  C,  ob- 
server; B,  body  observed. 

Q.  27 — What  is  declination  ? 

It  is  an  arc  of  the  celestial  meridian  between  the  object  and  the 
celestial  equator.  It  is,  in  reality,  the  celestial  latitude  of  the 
body,  and  corresponds  to  our  own  latitude.  See  Fig.  9.  Decl., 
declination. 

Fig.  9 
CELESTIAL  ^PHER-E 


Horizon 


Q.  28 — What  is  polar  distance? 

Polar  distance  is  an  arc  of  a  meridian  between  the  object  and  the 
pole  which  is  nearest  to  the  observer.  Thus,  if  the  latitude  of  the 
observer  should  be  North  and  the  declination  South,  then  it  would 
be  required  to  find  the  distance  from  the  North  pole,  which  would 
be  found  by  adding  the  declination  to  90° ;  but  if  both  the  declina- 
tion and  the  observer  were  Xorth  of  the  equator,  then  you  would 
subtract  the  declination  from  90°  to  get  the  distance  from  the 
nearest  pole.     See  Fig.  9.     0  D,  polar  distance. 

Q.  29 — What  is  meant  by  right  ascension? 

It  is  an  arc  of  the  celestial  equator  between  the  first  point  of 
Aries  and  the  meridian  passing  through  the  object.  It  is  in 
reality  the  celestial  longitude  of  the  object. 


278  Taylor's  Modern  Xavigatiox. 

Q.  30 — What  is  meant  by  dip.  or  depression  of  the  horizon  ? 

It  is  the  angle  between  the  visible  and  sensible  horizons,  caused 
by  the  elevation  of  the  observer  above  the  level  of  the  sea,  and  owing 
to  the  curvature  of  the  earth's  surface  it  depresses  the  horizon,  giv- 
ing the  observer  too  great  an  angle.  See  Fig.  6.  0  H,  visible 
horizon ;  0  S,  sensible  horizon,  angle  at  0  dip. 

Q.  31 — What  is  refraction? 

The  bending  of  a  ray  of  light  towards  the  vertical  as  it  passes 
through  the  atmosphere,  which  makes  an  object  appear  higher  than 
it  really  is. 

Fig.  lo 

REFRACTION 

5 


Note — The  exact  amount  of  refraction  is  very  hard  to  determine, 
but  the  approximate  amount  is  found  in  the  table  of  mean  refrac- 
tions for  a  certain  height  of  both  the  barometer  and  the  thermome- 
ter. This  element  will  make  even  the  best  of  observations  more 
or  less  in  doubt.  It  increases  in  its  amount  as  the  altitude  de- 
creases, and  decreases  in  its  amount  as  the  altitude  increases,  so 
that  when  the  sun  is  in  the  zenith  directly  above  your  head  the  re- 
fraction is  zero,  but  when  the  sun  is  near  the  horizon  it  is  a  con- 
siderable amount.  By  reference  to  the  table  of  refractions  this 
may  be  proven.  See  Fig.  10.  Black  lines,  apparent  place  of  body ; 
dotted  lines,  true  place  of  body;  P,  observer. 

Q.  32— What  is  parallax? 

Parallax  is  the  error  caused  in  an  observation  due  to  observing 
from  the  surface  of  the  earth  instead  of  from  its  center.  It  is  at 
its  greatest  amount  when  the  sun  is  on  the  horizon  and  smallest 
when  the  sun  is  in  the  zenith.  Even  when  the  sun  is  on  the  hori- 
zon it  is  so  small  an  amount  that  in  the  actual  practice  of  naviga- 
tion it  may  be  entirely  dispensed  with.  See  Fig.  11.  0,  body  ob- 
served ;  C,  center  of  earth ;  X,  observer ;  Z,  zenith. 


Definitions. 


279 


Q.  33 — What  is  semidiameter  ? 

Half  the  angular  diameter  of  the  sun.  It  is  used  to  reduce  an 
observation  to  the  center  of  the  sun.  The  amount  is  found  abreast 
of  the  date  on  Page  1  of  the  Nautical  Almanac,  and  from  a  practi- 
cal point  of  view  is  almost,  but  not  quite,  a  constant  quantity. 

Q.  34 — What  is  a  magnetic  meridian? 

A  magnetic  meridian  is  a  great  circle  in  whose  plane  lies  the 
compass-needle  when  not  affected  by  iron  in  the  vicinity  of  the 
compass.  See  Fig.  1.  Lines  from  M  P  to  M  P  are  magnetic 
meridians. 


Fig.  II 

PARALLAX 


Q.  35 — What  is  the  magnetic  equator? 

The  magnetic  equator  is  an  imaginary  circle  around  the  earth, 
where  a  needle  will  hang  perfectly  horizontal  when  it  is  suspended 
freely.    See  Fig,  1.    M  E,  C,  M  E,  magnetic  equator. 

Q.  36 — What  are  the  magnetic  poles? 

They  are  the  poles  on  the  earth's  surface,  towards  which  the  com- 
pass-needle points,  and  if  the  needle  is  freely  suspended  it  will 
hang  in  a  perfectly  upright  position.    The  dip  of  the  needle  on  the 


280  Taylor's  Modern  Navigation. 

magnetic  equator  is  zero,  and  at  the  magnetic  poles  is  90°.  The 
North  magnetic  pole  is  in  lafitude  70°  N.  and  longitude  97°  W., 
and  the  South  magnetic  pole  is  in  latitude  74°  S.  and  longitude 
147°  E.    See  Fig.  1.    M  P  and  M  P,  magnetic  poles. 

Q.  37 — What  is  a  true  course? 

A  true  course  is  the  angle  a  ship's  track  makes  with  a  true  meri- 
dian or  a  compass  course  corrected  for  deviation  and  variation. 
See  Fig.  1. 

Let  the  arrow  represent  course  of  ship,  and  the  angle  it  makes 
with  any  of  the  true  meridians,  will  be  the  true  course. 

Q.  38 — What  is  a  magnetic  course  ? 

A  magnetic  course  is  the  angle  a  ship's  track  makes  with  a  mag- 
netic meridian,  or  a  compass  course  corrected  for  deviation  or  what 
a  compass  would  indicate,  provided  there  was  no  deviation  what- 
ever on  it.  See  Fig.  1.  Arrow,  course  of  ship.  The  angle  it 
makes  with  the  magnetic  meridians,  will  be  the  magnetic  course. 

Q.  39 — What  is  a  compass  course? 

It  is  the  course  actually  shown  by  the  ship's  compass,  affected 
by  both  deviation  and  variation. 

Q.  40 — What  is  variation  of  compass? 

Variation  is  the  angle  between  the  true  meridian  and  the  mag- 
netic meridian,  or  the  amount  the  needle  iS  pulled  to  the  right  or 
the  left  of  the  true  north,  through  the  magnetism  of  the  earth.  It 
changes  as  the  ship  changes  her  position  on  the  surface  of  the 
earth,  and  changes  also  in  lapse  of  time.  Navigators  are  cau- 
tioned in  regard  to  this  matter,  as  in  some  parts  of  the  world  the 
annual  change  is  considerable,  making  it  dangerous  to  use  an  old 
magnetic  chart.  See  Fig.  1.  Angle  contained  between  any  line 
drawn  from  M  P  to  M  P   and  any  line  from  P  to  P. 

Q.  41 — What  is  deviation  of  compass? 

Deviation  is  the  error  of  the  compass  caused  by  the  iron  in  the 
ship,  and  is  the  amount  the  north  end  of  the  compass-needle  is 
pulled  to  the  right  or  left  of  the  magnetic  North.  It  changes  as 
the  direction  of  the  ship's  head  changes,  and  also  changes  as  the 
ship  alters  her  position  on  the  surface  of  the  rartli,  and  in  lapse  of 
time.  A  vessel  newly  launched  will  have  a  large  amount  of  devia- 
tion, which  will  gradually  diminish  and  set  down  to  what  is  called 
the  "saturation  point."  Deviation  (1iffer>  in  this  regard  from 
variation.  Variation  is  a  constant  amount  in  a  certain  position, 
whereas  deviation  is  n  different  amount  on  caeli  and  every  course. 


Definitions.  281 


Q.  42 — What  is  the  hour-angle  of  a  celestial  body? 
It  is  the  angle  at  the  pole  between  the  celestial  meridian  passing 
through  the  body  and  observer's  meridian.     See  Fig.  9. 

Q.  43 — What  is  the  observed  altitude? 

It  is  the  altitude  observed  with  the  sextant  and  corrected  for  the 
index  error,  if  any, 

Q.  44 — What  is  the  apparent  altitude? 

The  angular  height  of  an  object's  center  above  the  sensible  hori- 
zon. The  observed  altitude  corrected  for  dip  and  semidiameter 
gives  the  apparent  altitude.     See  Fig.  6. 

Q.  45— What  is  the  true  altitude  ? 

The  angular  height  of  an  object's  center  above  the  rational  hori- 
zon, or  it  is  the  observation  reduced  to  the  center  of  the  object  ob- 
served from  the  center  of  the  earth.  The  corrections  used  in  this 
case  are  refraction  and  parallax.     See  Fig.  6. 

Q.  46 — What  is  zenith  distance? 

It  is  the  distance  a  celestial  body  is  from  the  zenith,  which  is 
90°  from  any  part  of  the  horizon.  See  Fig.  9.  0  Z,  zenith  dis- 
tance. 

Q.  47 — What  is  an  azimuth? 

It  is  an  arc  of  the  horizon  between  the  meridian  which  passes 
tlirough  the  observer  and  the  vertical  circle  passing  through  the 
center  of  the  body.  It  is  reckoned  from  the  N.  or  S.  point  of  the 
horizon.     See  Fig.  9.     See  angle  at  Z. 

Q,  48 — What  is  meant  by  an  artificial  horizon  ? 

The  artificial  horizon  is  a  bowl  of  liquid  in  a  state  of  perfect  rest, 
such  as  a  tray  of  mercury,  and  is  used  in  the  following  manner: 
Place  the  artificial  horizon  on  a  table  or  box  directly  between  you 
and  the  body  to  be  observed.  Place  yourself  in  a  position  so  that 
you  can  sec  the  reflected  body  in  the  artificial  horizon.  Then  take 
the  sextant  and  bring  the  body  observed  down  to  touch  the  one 
which  is  seen  in  the  bowl.  This  will  give  just  twice  the  amount 
of  angle  required;  therefore,  divide  the  angle  and  you  will  get  the 
observed  altitude  of  the  body.     See  Fig.  7. 

Q.  49 — What  are  parallels  of  latitude  ? 

Parallels  of  latitude  are  small  circles  parallel  to  the  equator. 
Any  place  on  any  one  of  these  parallels  will  have  the  same  latitude. 
Fig.  1.     T  T  and  t  t. 


282  Taylor's  Modern  Navigation. 

Q.  50_ — What  is  dift'erenro  of  Intitude? 

Difference  of  latitude  is  an  arc  of  a  meridian  between  the  lati- 
tude of  any  two  places,  or  the  difference  of  latitude  is  the  distance 
a  ship  sails  to  the  true  North  or  South.     See  Fig.  1.    D  1  and  L  d. 

Q.  51 — What  are  meridional  parts? 

Meridional  parts  are  found  in  fable  3  of  most  epitomes.  They 
are  the  increase  in  the  size  of  a  degree  of  latitude,  corresponding  to 
the  separation  of  the  meridians.  The  reason  of  this  is  that  it  is 
used  in  the  problem  of  Mercator's  Sailing,  which  is  based  on  the 
supposition  that  the  world  is  fiat  instead  of  round.  The  proper  ex- 
planation of  this  problem  will  be  found  under  the  head  of  Mer- 
cator's Sailing.  (See  problem  of  Mercator's  Sailing  for  Fig.  Bow- 
ditch.) 

Q.  52— What  is  leeway  ? 

It  is  the  angle  between  the  ship's  wake  and  the  line  of  her  keel. 
To  ascertain  the  amount,  stand  on  the  fore  part  of  the  compass  and 
look  directly  astern.  Take  a  bearing  of  the  ship's  wake  and  note 
the  angle  between  the  fore-and-aft  line  and  the  trend  of  the  wake., 
and  you  will  have  the  amount  of  leeway  the  vessel  is  making. 

Q.  53 — What  is  civil  time,  or  civil  day? 

The  day  begins  at  midnight  and  ends  on  the  following  midnight. 
It  is  used  for  measuring  time  on  shore.     The  first  half  of  the  day 
is  called  a.m.^  or  ante-meridian,  the  other  half  being  called  p.m.,  or 
post-meridian. 
Q.  54 — What  is  astronomical  time? 

The  day  that  begins  at  noon  and  ends  on  the  following  noon, 
reckoned  through  24  hours.  In  the  practice  of  navigation  as- 
tronomical time  is  used,  as  all  the  elements  in  the  Nautical  Alma- 
nacs are  computed  for  the  astronomical  date,  or  noon  time.  There 
is  no  A.M.  or  p.m.  astronomical  time. 

Q.  55 — What  is  meant  by  sidereal  time? 

The  westerly  hour-angle  of  the  first  point  of  Aries ;  or,  in  other 
words,  it  is  the  time  shown  by  the  stars. 

Q.  56 — What  is  meant  by  mean  time? 

It  is  the  westerly  hour-angle  of  the  mean  sun.  The  mean  sun 
is  any  imaginary  sun  which  keeps  uniform  time,  which  the  true 
sun  does  not. 

Q.  57 — What  is  apparent  time? 

It  is  the  westerly  hour-angle  of  the  true  sun;  or,  in  other  words, 
the  time  shown  by  the  sun  which  we  see. 


Definitions.  283 


Q.  58 — What  is  meant  by  equation  of  time? 

It  is  the  diiference  in  time  between  the  place  of  the  true  sun  and 
that  of  the  mean  sun,  and  is  used  to  convert  mean  time  into  ap- 
parent time,  or  apparent  time  into  mean.  The  value  of  this  equa- 
tion of  time  is  found  on  pages  1  and  2  of  the  Nautical  Almanacs, 
and  the  sign  whether  to  add  or  to  subtract  is  given  on  the  top  of 
the  columns. 

Note — Four  times  a  year  it  is  at  its  greatest  amount,  namely,  on 
February  11th,  May  14th,  July  26th  and  November  3d;  and  four 
times  a  year  it  is  nothing,  namely,  on  April  loth,  June  15th,  August 
31st  and  December  24th. 

Q.  59 — Is  the  Pole-Star  situated  exactly  at  the  Pole? 

No;  it  is  about  1  1-3°  from  it. 

Q.  60 — What  is  the  best  time  for  taking  an  observation  to  find 
the  longitude? 

When  the  body  is  on  or  near  the  prime  vertical ;  in  other  words, 
when  it  bears  true  East  or  true  West. 

Q.  61 — What  is  a  chronometer? 

A  very  fine  watch  or  clock  compensated  with  a  temperature- 
balance,  and  protected  as  far  as  possible  from  sudden  jars  or 
shocks,  and  from  sudden  changes  of  temperature.  It  regis-ters  the 
Greenwich  Mean  Time  w^hen  correct. 

Q.  62 — What  is  the  length  of  a  nautical  mile? 

Six  thousand  and  eighty  feet. 


DIVISION  XII. 

KEEPING  THE  CHIEF  OFFICER'S  LOG-BOOK,  OR  SHIP'S 
JOURNAL. 

A  sample  page  of  which  will  be  found  on  page ,  at  the  end 

of  this  article.  The  keeping  of  this  book  and  the  writing  of  the 
proper  entries  is  one  of  the  important  duties  of  the  Chief  OfEicer. 

It  is,  however,  a  lamentable  fact  that  few  officers  take  a  suffi- 
cient amount  of  pride  in  keeping  the  book  neatly  or  accu- 
rately, and  when  one  considers  the  amount  of  importance  of  the 
log-book  in  relation  to  law-suits  for  insurance,  protests,  and  exten- 
sions, it  is  surprising  that  ship-masters  and  ship-owners  do  not 
more  vigorously  insist  that  the  book  be  properly  kept  and  written 
in  a  legible  manner.  Many  indolent  officers  do  not  attempt  to 
write  up  the  log  until  the  passage  is  nearly  ended.  It  will  thus, 
no  doubt,  be  easily  understood  that  many  matters  of  importance 
are  likely  to  be  omitted  unless  the  officer  has  an  excellent  memory. 

On  board  of  the  large  and  well-disciplined  ocean  liners,  the  log- 
book is  made  up  immediately  after  the  position  of  the  ship  has  been 
determined  at  noon,  each  officer  signing  abreast  of  liis  "watch,"  in 
a  column  provided  for  the  purpose.  After  this  has  been  done  the 
log-book  is  taken  to  the  master,  who,  after  examining  it  to  see  that 
the  proper  entries  are  made,  signs  it  himself  on  the  bottom  of  each 
page. 

This  is  an  excellent  rule,  the  chief  officer  having,  in  it,  a  check 
against  mistakes.  Should  he,  however,  discover  a  wrong  entry,  he 
m.ust  not  endeavor  to  erase  it,  but  should  draw  a  line  in  red  ink 
through  the  mistake  and  mark  his  initials  near  it. 

Tinder  no  circumstances  should  a  page  be  torn  from  the  log-book, 
for  if  a  log-book  should  be  so  mutilated  and  afterwards  offered  as 
evidence  in  a  lawsuit,  it  would  be  valueless,  if  detected  by  the  op- 
posing counsel. 

Log-slates,  so  much  in  use  formerly,  have  now  given  place  to 
the  rough  log-book.  This  book  is  generally  kept  in  the  wheelhouse 
for  the  making  of  entries  as  the  incidents  occur,  after  which  the 
entries  are  copied  into  the  chief  officer's  log-book. 

This  is  certainly  much  better  than  using  a  slate,  not  only  for  tlK 
health  of  those  concerned — for  slates  are  filthy  thing?  to  use — but 
whenever  a  slate  was  used  and  tlie  weather  at  all  damp  it  was  neces- 


Chief  Officeu's  Log-Book.  28") 

sary  to  place  the  slate  in  the  galley  oven  to  dry  before  the  writing 
became  legible. 

There  are  quite  a  number  of  different  arrangements  for  log- 
books, some  of  them  having  only  every  two  hours  printed,  making 
it  necessary  to  write  between  the  lines  very  frequently,  but  this  kind 
of  a  log-book  is  used  only  on  lumber-schooners,  whose  owners  prac- 
tice a  great  amount  of  false  economy.  All  log-books,  for  no  matter 
what  class  of  vessel,  should  devote  the  entire  left-hand  page  to  the 
civil  date,  arranged  so  that  the  noon  hour  comes  in  the  middle  of 
the  page,  with  the  necessary  spaces  for  entering  ship's  position  by 
either  dead-reckoning  or  observations,  the  upper  half  for  a.m.  and 
the  lower  half  for  p.m.  If  so  arranged,  the  whole  page  will  repre- 
sent a  civil  date,  and  from  i:he  middle  of  one  page  to  the  middle  of 
the  next,  an  astronomical  day.  This  arrangement  will  do  away 
with  confusing  the  civil  with  the  astronomical  day,  a  very  common 
occurrence  when  an  ancient  style  of  book  is  used.  The  opposite 
page  to  the  right  should  be  devoted  entirely  to  remarks  concerning 
observations,  passing  points  of  land,  making  or  taking  in  of  sail, 
state  of  weather,  and  all  other  items  relating  to  the  navigation  of 
the  ship. 

Some  officers  even  place  among  the  remarks  that  they  have  used 
a  fathom  or  so  of  spun  yarn,  and  such  foolish  items.  Such  remarks 
are  very  unnecessary,  yet  if  a  new  brace  were  rove  off,  or  sails  w'ere 
shifted  or  blown  away,  these  remarks  would  be  necessary. 

By  examining  the  sample  page  of  a  log-book  on  page ,  it  will 

be  noticed  that  a  column  is  devoted  to  the  giving  of  the  state  of  thi' 
weather  by  using  symbols.  This  is  an  excellent  plan.  It  saves 
trouble  and  space,  and  contributes  to  neatness.  The  system  is 
called  Beaufort's  Scale,  a  copy  of  wliich  is  here  given. 

Wind  is  also  indicated  by  nunibors  in  tlic  column  marked 
^•Force." 

WINDS. 

(Numerals  to  be  used  to  indicate  the  force  of  the  winds  as  ap- 
plied to  a  sailing-vessel  closehnulod  l)y  tlic  wind.) 

0— Calm. 

1 — Light  airs  (or  suflicient  to  give  steerage-way). 

2 — Light  breezes  (all  sail  may  be  carried  and  make  from  1  to  2 
knots  per  hour). 

3 — Grentle  breezes  (all  sail  may  be  carried  and  make  from  3  to  4 
knots  per  hour). 


286  Taylor's  Modern  Navigation. 

4 — Moderate  breezes  (all  sails  may  be  carried  and  make  from  5 
to  6  knots  per  hour). 

5 — Stiff  or  fresh  topgallant  breezes  (courses,  jib,  spanker,  whole- 
topsails  and  topgallantsails  may  be  carried). 

0 — Fresh  breezes  (topgallantsails  over  single-reefed  topsails, 
courses,  jib,  and  spanker  may  be  carried). 

7 — Fresh  breezes  (double-reefed  topsails,  whole  courses,  jib  and 
spanker  may  be  carried). 

8 — Moderate  gales  (three-reefed  fore  and  main,  close-reefed  miz- 
zentopsail  with  single-reefed  courses  and  foratopmast-staysail  may 
be  carried). 

9 — Strong  gales  (three-reefed  fore-and-main  topsail  with  close- 
reefed  courses  and  fore-storm  staysail  may  be  carried ) . 

10 — Gale  (close-reefed  maintopsail  and  close-reefed  foresail  with 
forestorm  staysail  may  be  carried). 

11 — Heavy  gale  (storm-sails  only  can  be  carried  or  close-reefed 
main  topsail  and  forestorm  staysail  or  staysails  only). 

12 — Hurricane  (no  sails  can  be  carried,  lying  to  or  scudding  un- 
der bare  poles). 

Symbols  to  Be  Used  in  Recording  the  State  of  the  Weather. 

b — Clear  blue  sky. 

e — Cloudy  weather. 

d — Drizzling  or  light  rain. 

f — Fog  or  foggy  weather. 

g — Gloomy,  or  dark,  stormy-looking  weather. 

h— Hail. 

1 — Lightning. 

m — Misty  or  liazy  weather. 

0 — Overcast. 

p — Passing  showers  of  rain. 

q — Squally  weather. 

r — Rainy  weather  or  continuous  rain. 

s — Snow,  snowy  weather,  or  snow  falling. 

t— Thunder. 

u — Ugly  appearance  or  threatening  weather. 

V — Variable  weather. 

w — Wet  or  heavy  dew. 


I  />g  of  S.  S.                                       From                                       Towartls 

. 

"Date                                                   y,ar                               Voya^  Mo. 

_^^ 

1 

1 

1 

g's;^^^.^s^s;i" 

0„.r„.. 

WIND. 

1 

1 

1 

B.»>,«T...           T,.r„UT,». 

thirstier. 

1 

I 

N.-.o.L»e.o..              VT 

Helgbt 

Thot. 

M 

% 

1 

A.M. 

n 

_____ 

1 

,, 

_____ 

10 

n 

^oon. 

I   Laliluda  bv                                                                                                            o         .         .. 

Latitude  by  observation                                                                                        " 

Longitude  by  observation                                                                                     " 

Latitude  by  D.R                                                                                                    o         .         .. 

Longitude  by  D.R.                                                                                                 "         ■         " 

Ikchei  of  Wateb  in  Weuj 

Course  made  good  sine*  preceding  noon  : 

Coi. 

Ccp. 

Co*. 

Distance  made  good  since  preceding  noon :                                                                                                                    miles. 

Distance  by  Log  since  preceding  noon  ;                                                                                                                  miles. 

Current  per  hour:                                 miles.  Bet                                trui- 

j 

(Longitude  by 

Frou 

Variation  ol  Compass: 

To 

Error  o(  compass  observed  at 

KEVOLUTIONS    rOR    li    HOUM 

DeviaUon  of  Compass  on 

- 

P.  M 

1 

2 

3 

4 

' 

6 

6 

~^      ' 

7 

' 

8 

9 

■ 

10 

11 

'    ^ 

Mid 

'~~~~~ 

Signatur,  of  Chitf  Offle*r                                                                                  Signatur*  of  Mtuttr 

~    " 

■"■»    In 

Commanded  by 

V-.- 

RECORD  OF  THE  MISCELLANEOUS  EVENTS  OF  THE  DAY 

___"" 

__,^_ 

. _^ 

H;^ 

— 

^jsino 

,hm,h 

,\:l. 

1 

.Frr 

-.alo 

■ 

1 





■     "^ 

-        ~ 

- — ' 

^ 

-^ 

Chief  Officer's  Log-Book.  287 

Symbols  to  Be  Used  in  Uecording  the  State  of  the  Sea. 

B — Broken  or  irregular  seas. 

C — Chopping,  short  or  cross  sea. 

G — Ground-swell. 

H — Heavy  sea. 

L — Long,  rolling  sea. 

M — Moderate  sea  or  swell. 

E — Rough  sea. 

S — Smooth  sea. 

T— Tide-rips. 

In  the  columns  for  barometer  and  thermometer  should  be  en- 
tered their  respective  readings,  for  by  them  future  weather  condi- 
tions may  be  anticipated  bv  the  experienced  mariner,  and  in  the 
case  of  the  thermometer  the  approach  of  ice  may  be  detected  by  a 
sudden  falling  in  temperature. 

All  entries  in  course  and  distance  columns,  with  the  variation  of 
the  locality  and  deviation  on  the  course  steered,  should  be  very  care- 
fully entered  in  a  plain  hand,  and  whenever  the  course  is  changed 
the  exact  time  should  be  noted,  with  the  reading  of  the  patent  log, 
if  one  is  in  use. 

If  foggy  weather,  the  exact  time  of  the  fog  shutting  down,  with 
any  alteration  in  speed  of  ship,  soundings,  and  the  time  of  weather 
clearing,  should  be  noted. 

A  special  entry  should  always  be  made  if  the  weather  is  boister- 
ous, after  the  following  manner:  "Ship  laboring  heavily,  and 
shipping  quantities  of  heavy  water."  This  entry  is  necessary,  for 
the  reason,  that  if  the  master  is  forced  by  circumstances  to  note  a 
protest  and  afterwards  to  extend  it,  before  being  able  to  collect  the 
insurance,  the  log-book  would  be  offered  as  evidence  of  bad  weather 
to  exonerate  the  ship  from  blame  in  regard  to  unseaworthiness,  etc. 

Side-lights  exhibited  from  sundown  to  sunrise,  pumps  strictly 
attended  to,  man  on  lookout,  with  the  temperature  and  amount  of 
water  in  the  holds,  are  also  very  important  entries. 

In  conclusion,  we  wish  to  emphasize  the  fact  that  carelessness  or 
untidiness,  or  downright  wilfullness,  in  regard  to  false  entries  will 
render  the  officers  keeping  the  book  liable  to  severe  censure,  and 
perhaps  be  the  means  of  the  revocation  of  his  certificate  as  an  officer. 


DIVISION  XIIL 

THE  OFFICIAL  LOG-BOOK. 

By  certain  acts  of  Congress,  every  vessel  making  voyages  from  a 
port  in  the  United  States  to  any  foreign  port  (except  ports  in  the 
British  North  American  possessions),  or,  being  of  the  burden  of 
seventy-five  tons  and  upwards,  from  a  port  on  the  Atlantic,  to  a 
port  on  the  Pacific,  or  vice  versa,  shall  have  an  official  log-book, 
and  every  Master  of  such  vessel  shall  make  or  cause  to  be  made 
therein,  entries  of  the  following  matters,  that  is  to  say : 

First.  Every  legal  conviction  of  any  member  of  his  crew,  and 
the  punishment  inflicted. 

Second.  Every  ofEense  committed  by  any  member  of  his  crew 
for  which  it  is  intended  to  prosecute  or  to  enforce  a  forfeiture, 
together  with  such  statement  concerning  the  reading  over  such 
entry,  and  concerning  the  reply,  if  any,  made  to  the  charge,  as  is 
required  by  the  provisions  of  Section  4597, 

Third.  Every  offense  for  which  punishment  is  inflicted  on 
board,  and  the  punishment  inflicted. 

Fourth.  A  statement  of  the  conduct,  character  and  qualifica- 
tions of  each  of  his  crew;  or  a  statement  that  he  declines  to  give 
an  opinion  of  such  particulars. 

Fifth.  Every  case  of  death  happening  on  board,  with  the  nature 
thereof  and  the  medical  treatment. 

Sixth.  Every  case  of  death  happening  on  board,  with  the  cause 
thereof. 

Seventh.  Every  birth  happening  on  board,  with  the  sex  of  the 
infant  and  the  names  of  the  parents. 

Eighth.  Every  marriage  taking  place  on  board,  with  the  names 
y.nd  ages  of  the  parties. 

Ninth.  The  name  of  every  seaman  or  apprentice  who  ceases  ta 
be  a  member  of  the  crew  otherwise  than  by  death,  with  the  place, 
time,  manner,  and  cause  thereof. 

Tcntli.  The  wages  due  to  any  seaman  or  apprentice  who  dies 
during  the  voyage,  and  the  gross  amount  of  all  deductions  to  be 
made  therefrom. 

Eleventh.  The  sale  of  the  effects  of  any  seaman  or  apprentice 
who  dies  during  the  voyage,  including  a  statement  of  each  article 
sold,  the  sum  received  for  it. 


Metkorological  Log.  289 


2\celftli.  In  every  case  of  collision  in  which  it  is  practicable  so 
to  do,  the  master  shall,  immediately  alter  the  occurrence,  cause  a 
statement  thereof,  and  of  the  circumstances  under  which  the  same 
occurred,  to  be  entered  in  the  official  log-book.  Such  entry  shall 
be  made  in  the  manner  prescribed  in  Section  4291,  and  failure  to 
make  such  entry  shall  subject  the  offender  to  the  penalties  pre- 
scribed by  Section  4292. 

Instructions  in  regard  to  all  entries  are  printed  in  the  first  part 
of  the  book,  with  the  most  recent  laws  governing  merchant  seamen, 
payment  of  wages,  food,  signing  on  and  discharging  the  crew,  etc. 

The  book  is  supplied  to  masters  by  the  United  States  Shipping 
Commissioners  when  signing  the  crew,  and  delivered  to  them  again 
at  the  expiration  of  the  voyage. 

Masters  should  be  careful,  however,  to  have  all  entries,  no  mat- 
ter of  what  nature,  properly  witnessed  and  signed  by  at  least  two 
members  of  the  crew,  to  prevent  argument  at  tlTe  time  of  paying 
off.  and  to  save  the  ship  from  expenses. 

THE  METEOROLOGICAL  LOG.  OR  WEATHER  REPORT. 

The  proper  keeping  of  this  record  is  of  the  utmost  importance, 
and  one  that  should  be  more  frequently  and  accurately  kept  than  it 
is  at  the  present  time,  for  by  it  future  weather  conditions  are  pre- 
dicted or  foretold,  and  conditions  peculiar  to  certain  localities  may 
be  recorded  and  charted  for  the  future  use  and  benefit  of  the  mari- 
ner. 

It  is  a  deplorable  fact,  when  one  considers  the  importance  of 
weatherology,  that  the  log  is  rarely  kept  on  xlmerican  vessels  out- 
side of  ocean  liners,  the  licensed  (  ?)  officers  of,  particularly,  sailing- 
vessels  and  cargo-steamers,  entirely  ignore  the  earnest  request  of 
the  United  States  Hydrographic  Office,  for  the  reason  that  they 
think  the  keeping  of  the  record  is  "fancy  navigation,"  and  so  diffi- 
cult that  it  requires  an  exceedingly  high  degree  of  intelligence  and 
a  college  education,  entailing  a  considerable  waste  of  time,  and 
consequent  loss  of  sleep,  if  the  form?  have  to  be  filled  out  during 
the  watch  below. 

This  is  not  so,  for  the  forms  supplied  to  record  the  required  in- 
cidents and  conditions  of  weather  are  arranged  in  so  simple  a  man- 
ner that  even  a  half-witted  person  could  almost  understand  how  to 
fill  them  out,  and  the  length  of  time  required  to  do  the  same  would 
not  occupy  more  than  five  minutes  even  for  a  poor  penman. 
Taylor's  Mod.  Nav.  19. 


290  Taylor's  Modern  Navigation. 

If  it  is  the  wish  of  the  master  that  a  log  of  this  kind  should  be 
kept  on  board  of  his  vessel,  he  should  first  procure  the  necessary 
forms  from  the  nearest  branch  Hydrographic  Office  and  designate 
one  of  the  junior  officers  for  the  purpose,  with  instructions  that  the 
entries  must  be  made  with  regularity,  neatness,  and  precision,  and 
that  the  same  be  submitted  to  him  for  approval,  as  regularly  as  the 
chief  officer's  log-book. 

All  instruments  used  for  the  purpose,  such  as  barometers,  ther- 
mometers, etc.,  should  be  compared  and  adjusted  as  frequently  as 
possible,  especially  whenever  the  vessel  is  in  a  port  where  there  is 
a  branch  Hydrographic  Office,  as  the  officers  in  charge  have  stand- 
ard instruments  on  hand  for  the  purpose  of  comparison,  the  same 
Ijeing  free  of  cost  to  the  navigator. 

If  there  is  any  error,  it  should  be  noted,  and  if  it  reads  too  high 
or  too  low,  all  readings  must  be  reduced  to  the  standard  l)efore  the\ 
can  be  utilized. 

All  the  necessary  information  for  intending  observers,  with  the 
blank  forms  for  recording  events,  wind,  current,  and  pilot-charts, 
may  be  procured  from  the  officers  in  charge  of  the  local  office,  free 
of  cost,  they  being  only  too  anxious  to  supply  any  information  that 
they  possess,  and  will  courteously  acknowledge,  by  letter,  the  re- 
ceipt of  the  same  from  any  contributor. 

The  blank  forms  are  made  up  in  about  the  size  of  an  ordinary 
receipt-book.  On  the  first  page,  inside  of  the  cover,  will  be  found 
instructions  to  recorders,  relating  to  the  time  of  observation.  This 
is  important,  as  the  Office  wishes  observations  to  be  taken  when  it 
is  mean  noon  at  (ireenwich,  so  that  they  will  all  be  simultaneous. 

Synil)ols  are  used  to  indicate  the  weather,  strength  of  wind  and 
sea,  the  same  as  already  explained  under  the  heading  of  Chief  Of- 
ficer's Log-Book,  but,  in  addition  to  this,  cloud-classifications  must 
also  be  used,  the  following  being  the  official  description.  The  United 
States  government  has,  however,  on  this  subject,  published 
colored  plates  illnstrating  the  different  cloud-formations. 

The  following  cloud-rornis  are  arranged  according  to  a  general 
descending  scale  of  altitude,  observation  having  shown  that  there 
are  live  main  eloud-levels,  viz..  cirrus  (highest),  cirro-cumulus, 
alto-cnmnlus.  cnmnliis,  and  strains   (lowest). 

1.  Cirrus  (Ci.) — Detached  clouds,  delicate  nnd  fibrous-looking, 
taking  the  form  of  feathers,  generally  of  a  white  color,  sometimes 
arranged  in  belts  which  cross  a  ))ortiun  <if  the  sky  in  great  circles, 


Mete()kologicaj>  Lot;.  291 


and,  by  an  effect  of  periipective,  converge  toward  one  or  two  oppo- 
site points  of  the  horizon.  (The  Ci.-S.  and  the  Ci.-Cu.  often  con- 
tribute to  the  formation  of  these  belt.--.) 

2.  Cirro-;Stratus  {Ci.-S.) — A  thin,  wliitish  slieet.  at  times 
completely  covering  the  «ky,  and  only  giving  it  a  wliitish  appear- 
ance (it  is  then  sometimes  called  cirronel)ula),  or  at  others  present- 
ing, more  or  less  distinctly,  a  formation  like  a  tangled  web.  This 
sheet  often  jirodnces  halos  around  the  sun  and  moon. 

3.  ('irro-Cuiiiuliis  (Ci.-Cu.) — Small  globular  masses,  or  white 
flakes  without  shadows,  or  having  very  slight  shadows,  arranged  in 
groups  and  often  in  lines. 

4.  Alto-Cumulus  (A.-Cu.) — liather  large  globular  masses, 
white  or  grayish,  partially  shaded,  arranged  in  groups  or  lines,  and 
often  so  closely  packed  that  their  edges  appear  confused.  The  de- 
tached masses  are  generally  larger  and  more  compact  (changing  to 
S.-Cu.)  at  the  center  of  the  group;  at  the  margin  they  form  into 
finer  flakes  (changing  to  Ci.-Cu.).  They  often  spread  themselves 
out  in  lines  in  one  or  two  directions. 

5.  Alto-Stratus  {A.-S.) — A  thick  sheet  of  a  gray  or  bluish 
eolor,  showing  a  brilliant  patch  in  the  neighborhood  of  the  sun  or 
moon,  and  which,  without  causing  halos,  may  give  rise  to  coronae. 
This  form  goes  through  all  the  changes  like  the  Cirro-Stratus.  but 
by  measurements  made  at  Upsala,  its  altitude  is  one-half  less. 

6.  Strato-Cumulus  (S.-Cu.) — Large  globular  masses  or  rolls  of 
dark  cloud,  frequently  covering  the  whole  sky,  especially  in  winter, 
and  occasionally  giving  it  a  wavy  appearance.  The  laj'er  of  Strato- 
Cumulus  is  not,  as  a  rule,  very  thick,  and  patches  of  blue  sky  are 
often  visible  through  the  intervening  spaces.  All  sorts  of  transi- 
tions between  this  form  and  the  Alto-Cumulus  are  noticeable.  It 
may  be  distinguished  from  Ximbus  by  its  globular  or  rolled  ap- 
pearance, and  also  because  it  does  not  bring  rain. 

7.  Nimhiis  (N.),  Faiti-Clouds — A  thick  layer  of  dark  clouds, 
without  shape  and  with  ragged  edges,  from  which  continued  rain 
or  snow  generally  falls.  Througli  the  openings  of  these  clouds  an 
upper  layer  of  Cirro-Stratus  or  Alto-Stratus  may  almost  invariably 
be  seen.  If  the  layer  of  Nimbus  separates  into  shreds,  or  if  small 
loose  clouds  are  visible  floating  at  a  low  level,  underneath  a  large 
Nimbus,  they  may  be  described  as  Fracto-Nimbus  (Fr.-N.),  "scud" 
of  sailors. 


292  Taylor's  Modern  Navigation. 


8.  Cumulus  (Cu.),  ^Yoolpacl^  C/owt^s— Thick  clouds  of  which 
the  upper  surface  is  dome-shaped  and  exhibits  protuberances,  while 
the  base  is  horizontal.  These  clouds  appear  to  be  fornied  by  a 
diurnal  ascensional  movement  Avhich  is  almost  always  observable. 
When  the  cloud  is  opposite  the  sun,  the  surfaces  usually  presented 
to  the  observer  have  a  greater  brilliance  than  the  margins  of  the 
protuberances.  When  the  light  falls  aslant,  these  clouds  give  deep 
shadows;  when,  on  the  contrary,  the  clouds  are  on  the  same  side 
as  the  sun,  they  appear  dark,  with  bright  edges. 

The  true  Cumulus  has  clear  superior  and  inferior  limits.  It  is 
often  broken  up  by  strong  winds,  and  the  detached  portions  un- 
dergo continual  changes.  These  may  be  distinguished  by  the  name 
of  Fracto-Cumulus  (Fr.-Cu.). 

Cumulus  sometimes  presents  a  mammillated  lower  surface.  It 
is  then  called  Mammato-Cumulus  (M.-Cu.) 

9.  Cumulo-Nimhus  (Cu.-N.),  the  Thunder-cloud ,  Shower- 
Cloud — Heavy  masses  of  clouds  rising  in  the  form  of  mountains, 
turrets,  or  anvils,  generally  having  a  sheet  or  screen  of  fibrous  ap- 
pearance above  ("false  Cirrus"),  and  underneath,  a  mass  of  cloud 
similar  to  "Nimbus."  From  the  base  there  usually  fall  local 
showers  of  rain  or  of  snow  (occasionally  hail  or  soft  hail).  Same- 
times  the  upper  edges  have  the  compact  form  of  Cumulus,  forming 
into  massive  peaks,  round  which  the  delicate  "false  Cirrus"  floats, 
and  sometimes  the  edges  themselves  separate  into  a  fringe  of  fila- 
ments similar  to  that  of  the  Cirrus  cloud.  This  last  form  is  par- 
ticularly common  in  spring  showers. 

The  front  of  thunder-clouds  of  wide  extent  frequently  presents 
the  form  of  a  large  bow  spread  over  a  portion  of  the  sky,  which  is 
uniformly  brighter  in  color. 

10.  Stratus  (S.) — A  horizontal  sheet  of  lifted  fog.  When  this 
sheet  is  broken  up  into  irregular  shreds  by  the  wind,  or  by  the  sum- 
mits of  mountains,  it  may  be  distinguished  by  the  name  of  Fracto- 
Stratus  (Fr.-S.). 

]\TQte — The  attention  of  mariners  is  esi)ecially  called  to  the  value 
of  observations  of  cirrus,  as  this  form  of  cloud  is  often  closely  con- 
nected with  barometric  depressions.  If  the  cirrus  occur  in  radiat- 
ing bands  crossing  the  sky,  the  point  of  convergence  of  these  bands 
should  be  noted ;  if  in  the  form  of  a  cloud-bank,  or  sheet,  upon  the 
horizon,  the  center,  or  point  of  greatest  density  of  this  bank,  as 


Meteorological  Log.  293 

this  point  will  sometimes  serve  to  indicate  in  a  general  manner  the 
direction  of  the  center  of  an}'  cyclonic  disturbance. 

Great  care  should  be  taken  when  recording  the  cloud-forms  with 
the  direction  from  which  it  is  moving  and  its  approximate  altitude, 
as  it  will  often  be  of  great  value  to  the  mariner  regarding  a  shift  of 
wind,  and  assist  him  to  interpret  the  strange  behavior  of  the 
barometer;  this  would  be  especially  useful  if  in  a  locality  where 
circular  storms  were  prevalent,  as  it  would  serve  to  indicate  the 
probable  direction  from  which  the  wind  would  be  first  experienced. 

[Xotc — For  theory  of  cireuhir  storms  see  Bowditch,  as  it  is  not 
the  intention  to  give  an  exhaustive  account  of  them  in  this  book.) 

The  accompanying  forms,  numbered  here  for  the  sake  of  easy 
reference,  are  duplicates  of  those  supplied  by  the  U.  S.  Hydro- 
graphic  Office  to  observers. 

Form  Xo.  1  is  a  sample  page  showing  the  space  for  entries  under 
ordinary  conditions,  with  cloud  diagrams,  to  illustrate  the  motion 
and  altitude  of  clouds. 


294 


Taylor's  Modern  Navigation. 


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Special  care  should  be  taken,  when  uue  of  tliese  storms  is  en- 
counted,  to  record  each  change  in  tlie  direction  of  the  wind,  sea, 
force,  weather,  clouds,  and  especially  the  behavior  of  the  barometer 
with  the  change  of  ship's  course,  remembering  that  all  these  ob- 
servations, with  the  data  collected  from  other  sources,  a  storm 
theory  may  be  evolved  for  the  benefit  of  seamen  who  may  subse- 
quently be  navigating  in  the  same  vicinity,  and  should  any  inci- 
dents or  phenomena  occur  which  are  of  note,  it  is  the  duty  of  the 
mariner  to  forward  a  written  account  of  the  same  to  the  nearest 
Branch  Hydrographic  Office. 

Form  No.  4  is  for  recording  the  appearance  of  ice,  and  is  very 
important,  for  the  reason  of  the  necessity  of  cautioning  other  vessels 
that  ice  may  be  found  in  a  certain  vicinity  at  certain  times  of  the 
year.  By  examining  a  great  number  of  reports  of  this  kind  a  very 
good  idea  can  be  arrived  at  in  regard  to  what  time  of  the  year  to  be 
on  the  lookout. 

The  passing  of  wrecks,  driftwood,  etc.,  should  also  be  entered  on 
the  form,  with  a  short  description  of  the  same,  latitude,  longitude, 
etc.,  for  by  these  means  ocean  currents  may  be  determined,  and  in 
the  case  of  derelict  vessels  the  position  may  be  published  from  time 
to  time,  so  thnt  the  navigator  may  be  placed  on  his  guard. 


298 


Taylor's  Modern  Navigation, 


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CllKONOilETEU.  299 


When  one  considers  the  immense  expense  and  the  amount  of  or- 
ganized intelligence  required  to  provide  the  navigator  with  impor- 
tant information,  so  that  he  may  navigate  his  vessel  with  a  greater 
degree  of  safety,  it  is  surprising  that  they  do  not,  as  a  body,  take 
more  interest  and  work  with  more  enthusiasm  to  supply  the  Hydro- 
graphic  Office  with  data,  so  that  the  same  may  be  arranged  and 
tabulated  in  a  scientific  numner,  eventually  to  be  returned  to  them 
for  their  guidance. 

There  is  no  country  in  the  world  outside  of  the  United  States 
where  so  valuable  a  mass  of  information  is  supplied  free  of  cost  to 
the  mariner;  therefore  it  is  plainly  their  moral  duty  to  assist  those 
who  assist  them  to  their  utmost. 

THE  CHKOXOMETEE. 

Handling — Too  much  care  cannot  be  taken  in  handling  this  very 
necessary  and  important  instrument  of  navigation,  as  the  follow- 
ing article  will  make  apparent,  for  there  is  no  doubt  that  many 
vagaries  or  erratic  errors  are  caused,  through  ignorance,  from  care- 
less handling. 

Inexperienced  persons,  not  having  a  sufficient  amount  of  knowl- 
edge regarding  the  importance  of  careful  handling,  will  not  even 
take  the  trouble  to  secure  the  gimbals  with  the  stay  provided  in 
every  chronometer  for  that  purpose,  when  carrying  it  to  or  from 
the  ship.  This  is  wrong;  for  by  suddenly  or  sharply  turning  a 
corner,  it  may  be  so  jarred  that  the  delicate  interior  may  be  so  dis- 
arranged or  interfered  with,  that  it  may  even  stop  for  a  while,  and 
afterwards  by  giving  it  another  sharp  twist  it  may  start  again.  If 
this  is  done,  and  the  careless  carrier  should  deliver  it  to  the  un- 
suspecting master  with  the  error  and  rate  it  had  when  leaving  the 
shop  (which  has  been  totally  changed  by  the  rough  handling),  the 
master  with  all  confidence  would  receive  it  and  attempt  to  navigate 
his  vessel,  thereby  the  result  being  that  a  most  unaccountable  error 
would  be  detected  eventually  and  perhaps  the  loss  of  the  vessel 
might  occur. 

The  chronometer  makers  or  repairers  should  therefore  see  to  it 
tliat  the  person  to  whom  the  chronometer  is  intrusted  to  take  'from 
or  deliver  the  chronometer  to  a  vessel,  is  one  having  full  knowledge 
of  his  responsibility;  for  no  matter  how  careful  the  people  are  in 
the  shop,  or  what  their  reputation  for  care  and  skillful ness  may  be, 
it  is  liable  to  be  entirely  ruined  by  carelessness  in  delivering. 

Care  on  Board — The  chronometer  should  be  placed  in  an  outside 


300  Taylor's  Modern  Xavigatiox. 


box  having  its  interior  cushioned  with  hair,  to  diminish  the  risk  of 
alteration  of  the  rate  from  sudden  jars  by  a  heavy  sea  striking  the 
ship,  or  from  bumping  violently  against  a  dock.  The  box  will  also 
be  of  considerable  benefit  in  protecting  the  chronometer  from  moist- 
ure and  vapor  arising  from  cargoes. 

When  selecting  a  position  to  keep  the  chronometer  for  easy  access 
when  taking  observations,  it  should  at  the  same  time  be  so  placed 
where  it  will  not  be  exposed  to  sudden  changes  of  temperature,  such 
as  near  a  door  or  companionway,  whereby,  if  opened,  the  salt  sea 
breeze  or  spray  may  dash  in  upon  it,  for  by  this  the  air  in  the  in- 
terior may  become  condensed,  causing  perhaps  a  minute  particle 
of  rust  to  form  on  the  works,  seriously  affecting  the  rate.  This  has 
frequently  occurred,  causing  the  navigator  considerable  uneasiness. 

It  should  also  be  placed  as  far  as  possible  from  magnetic  sub- 
stances, such  as  iron,  a  compass,  or  adjusting  magnets,  as  the  fol- 
lowing will  illustrate: 

A  certain  young  man,  whose  name  is  witliheld  for  obvious  rea- 
sons, having  been  appointed  master  of  a  coasting  lumber  vessel, 
was  extremely  particular  in  regard  to  the  vessel's  equipments,  such 
as  ropes,  blocks,  sails,  etc.,  but  neglected  entirely  those  instruments, 
namely,  the  chronometer  and  compass,  whereon  the  safe  navigation 
of  his  vessel  entirely  depended. 

This  man  came  to  the  writer  on  his  arrival  after  completing  his 
first  voyage,  and  complained  that  the  chronometer  (he  had  only  one 
on  board)  had  acted  very  strangely,  in  fact,  the  ship's  position  was 
found  to  be  about  36  miles  in  error  when  making  port.  Not  having 
time  to  visit  his  vessel,  I  advised  him  to  send  the  chronometer  to  a 
reputable  person  for  repairs  and  cleaning,  as  it  was  of  doubtful 
age,  and  there  was  no  record  of  the  last  time  it  was  cleaned.  He 
took  my  advice,  leaving  it  on  shore  and  taking  another  one  in  its 
place,  yet  on  his  return  from  his  second  voyage  he  reported  the 
same  occurrence.  I  therefore  made  a  special  visit  to  the  vessel  and 
found  that  the  compass  used  for  steering  was  situated  in  a  little 
"cubby  hole"  cut  into  the  after  part  of  the  deck-house,  the  cap- 
tain's cabin  being  situated  in  the  same  part  of  tlie  house:  he  had 
fixed  the  chronometer  on  a  shelf  to  the  after  wall  of  his  cabin,  with- 
in two  feet  of  the  compass. 

We  immediately  changed  the  position  of  the  chronometer  to  the 
fore  part  of  the  cabin  and  afterwards  there  was  no  complaint,  for 
the  obvious  reason  that  it  was  at  a  reasonable  distance  from  a  mag- 
netic substance. 


CliKOXOMETER.  301 


This  incident,  it  is  to  be  iioped,  will  caution  the  intelligent 
reader. 

•    More  Than  One  Ckrunonieter  Xecessary. 

Vessels  making  long  voyages  should  have  not  less  than  three 
chronometers  on  board  and  in  the  case  of  a  large  ocean  steamer 
there  ought  to  be  another  one  for  the  exclusive  use  of  the  officers, 
situated  in  the  officers'  mess  room  or  some  other  convenient  place 
of  easy  access. 

If  only  one  is  on  board  and  any  accident,  such  as  running  down, 
breaking  or  clogging  of  the  works,  or  if  it  suddenly  changes  its  rate, 
the  navigator  is  placed  in  a  very  awkward  position,  endangering 
the  lives  and  property  under  his  charge,  especially  if  navigating  in 
the  vicinity  of  a  group  of  islands  or  shoals,  such  as  those  found  in 
the  Pacific  Ocean. 

If  there  are  two  chronometers  on  board  it  is  certainly  better  than 
one,  especially  if  one  should  run  down,  etc.,  still  the  navigator 
would  not  be  very  much  better  off,  for  if  one  of  them  should  change 
its  daily  rate  it  would  be  very  difficult,  in  fact  absolutely  impossible, 
to  tell  which  of  the  two  was  wrong. 

But  if  three  are  on  board  and  one  goes  wrong,  there  are  two 
others  for  a  check  to  tell  which  one  it  is,  providing,  however,  that 
the  navigator  is  careful  to  compare  the  three,  and  note  the  errors 
every  day  and  enter  the  same  in  a  book  kept  especially  for  the  pur- 
pose, a  sample  of  which  is  attached  to  this  article. 

We  cannot,  however,  expect  a  coasting  schooner  to  carry  three 
chronometers,  in  fact  it  is  not  really  necessary,  as  the  masters  of 
such  vessels  have  plenty  of  opportunity  to  verify  ship's  position  by 
bearings  of  the  land.  They  should,  however,  carry  one  if  the 
owner  is  a  particularly  liberal  person,  yet  if  he  is  not,  the  master 
^l■ould  carry  one  himself  at  his  own  expense,  to  keep  his  hand  in 
and  not  get  rusty. 

It  is  the  opinion  of  the  author  tliat  marine  insurance  com- 
panies should  insist,  before  writing  a  policy,  that  vessels  be  prop- 
erly supplied  with  a  sufficient  number  of  chronometers,  according 
to  the  prospective  voyage,  the  risk  would  be  sensilily  diminished. 

Wimding. 

On  the  under  side  of  the  bowl  will  be  found  a  hole  in  a  movable 
plate,  which  covers  the  keyhole  in  the  bowl  when  not  winding,  to 
prevent  the  dust  or  moist  atmosphere  from  entering  the  bowl  itself. 


303  Tavlok"s  Modern  Navigation. 

If  it  is  the  intention  to  wind,  open  the  box  gently — do  not  shim 
the  lid — take  the  bowl  in  left  hand  and  turn  it  upside  down,  slew 
the  plate  around  until  the  keyhole  is  seen,  then  insert  the  key. 

Turn  the  key  easily,  do  not  jerk  it,  until  the  winding  is  stopped 
short ;  then  remove  the  key,  see  that  the  plate  covers  the  keyhole, 
and  let  the  bowl  gently  resume  its  proper  position — do  not  let  go 
with  a  jerk — then  close  the  box. 

If  the  key  slips  when  winding,  it  is  proof  that  you  are  turning 
the  wrong  way,  and  to  prove  that  it  is  wound,  examine  the  little 
dial  on  the  face  of  the  chronometer.  If  the  hand  points  to  tviniL 
it  is  not  wound;  if  it  points  to  up,  it  is  wound.  If  it  is  between 
wind  and  down,  it  is  past  the  time  for  winding.  This  should 
never  occur,  as  it  may  cause  an  alteration  in  the  daily  rate. 

Wind  at  the  same  time  each  day.  Do  it  yourself,  or  one  of  the 
officers.  Do  not  appoint  the  cook  or  steward  for  this  important 
dut}",  for  they  are  likely  to  l)e  in  too  much  of  a  hurry,  and  l)ang 
things  around,  if  they  smell  something  burning  on  the  stove. 

The  Best  Kind  of  Chronometers 

Are  those  commonly  called  two-day,  but  wdiich  in  reality  run  56 
hours;  those  called  eight-day  are  not  so  reliable,  as  the  tension  on 
the  works  diminishes  the  nearer  it  approaches  down,  unless  bal- 
anced to  counteract.  If  either  a  two-  or  eight-day  chronometer  is 
used,  it  should  be  wound  regularly  each  day,  especially  if  the  eight- 
day  is  not  properly  balanced. 

One  of  the  great  objections  to  the  eight-day  chronometer  is  the 
liability  of  a  person  to  forget  to  wind  on  the  proper  day  and  perhaps 
let  it  run  down  altogether.  Should,  however,  the  chronometer  run 
down,  and.  after  winding  it  up,  it  refuses  to  start,  give  it  a  quick 
eiicular  horizontal  motion  until  it  does. 

Rating. 

Under  the  heading  of  "Longitude  by  Chronometer,"  the  methods 
of  finding  the  daily  and  accumulated  rate  have  been  thoroughly  ex- 
plained, therefore  we  will  only  discuss  the  different  methods  and 
facililies  for  finding  the  total  error  on  a  certain  date. 

First  Method — At  all  important  seaports  of  the  world  there  are 
time  signals  for  finding  the  error  of  the  chronometer.  Sometimes 
it  is  the  firing  of  a  gnu,  collapsing  of  a  cone  or  the  dropping  of  a 
ball,  either  nno  of  ilu'  signals  being  made  at  iMean  Xoon  at  place 


ClIKONO-MKTEH.  .  303 


for  a  standard  ]\Ieri(lian.  By  watching  the  signal  and  noting  the 
instant  of  time  by  the  chronometer,  the  error  for  the  particidar  day 
of  observation  will  be  determined,  but  as  sometimes  the  mechanism 
of  the  signal  may  get  out  of  order,  and  thereby  not  made  at  the 
proper  instant,  the  othcer  in  charge  always  notifies  the  daily  papers, 
so  that  the  navigator,  by  reference  to  the  same,  may  know  if  the 
signal  was  made  at  the  proper  instant. 

Second  Metliod — The  error  of  the  chronometer  may  be  deter- 
mined with  tolerable  accuracy  wlien  in  the  vicinity  of  land  well  sur- 
veyed and  charted,  by  the  following  rule,  providing  a  number  of 
observations  are  taken,  worked  out  separately  and  the  true  place  of 
the  horizon  well  defined,  but  as  the  last  item  is  as  a  rule  so  doubt- 
ful, any  error  found  by  observing  above  the  sea  horizon  must  be 
used  with  caution;  still,  if  a  vessel  has  made  a  long  voyage,  it  will 
certainly  be  a  very  useful  check. 

Rule — Locate  the  ship's  position,  latitude  and  longitude,  very 
carefully  by  taking  bearings  of  the  land,  and  at  same  instant  take 
one  or  more  sights,  the  same  as  when  taking  an  observation  to  as- 
certain the  longitude,  apply  the  assumed  error  of  chronometer, 
work  out  and  find  the  longitude.  If  this  longitude  coincides  with 
the  one  found  by  bearings  of  the  land,  the  error  assumed  will  \ye 
correct ;  if  not,  the  assumed  error  will  be  incorrect  to  the  amount  of 
the  difference  of  longitude  in  time  between  the  correct  and  incor- 
rect longitude. 

Or,  to  the  Mean  Time  at  ship  found  by  working  the  sight,  apply 
the  longitude  of  the  place  in  time.  If  East  subtract,  if  West  add. 
The  result  will  be  the  correct  Greenwich  Mean  Time.  Take  the 
difference  between  it  and  the  time  shown  by  chronometer.  The  re- 
sult will  be  the  total  error  for  that  date. 

Slow  if  the  chronometer  time  is  less  than  G.M.T. 

Fast  if  the  chronometer  time  is  more  than  G.M.T. 

As  previously  remarked,  a  correct  result  will  depend  on  the  true 
place  of  the  horizon  and  also  the  amount  of  care  taken  when  ob- 
serving. 

If  practicable  and  tlie  ship  is  provided  with  an  artificial  horizon, 
it  would  be  much  better  to  land  and  make  the  observation,  taking 
two  stars,  one  to  the  East  and  other  to  the  West,  in  preference  to 
the  sun.  working  each  sight  separately.  The  result  in  tliis  case 
would  be  entirely  reliable. 

There  are  several  other  methods  of  finding  tbe  error,  principally 
the  problem  of  erpial  altitude  and  the  transit  of  a  lieaveiily  l)ody.  and 


304  Taylor's  Modern  Xavigatiox. 

although  they  are  theoretically  correct,  in  actual  practice,  for  the 
ordinary  navigator,  they  are  entirely  unreliable. 

To  obtain  the  daily  rate  of  a  chronometer  it  would  be  necessary 
to  determine  the  error  on  two  dates  about  six  or  seven  days  apart 
by  either  of  the  methods  here  given,  or  by  comparison  with  a 
standard  chronometer  such  as  may  be  found  in  the  Branch  Hydro- 
graphic  Offices  in  the  United  States,  the  difference  of  the  error 
divided  by  the  number  of  days  giving  the  daily  rate. 

Rates  of  Chronometer. 

Shop  rates  given  by  "shopticians"  are  as  a  rule  unreliable  for  use 
at  sea,  owing  to  the  difference  of  location  and  the  liability  to  change 
by  carrying  from  shop  to  ship,  and  change  of  temperature.  Shop 
rates  as  given  to  the  navigator  on  printed  slips  rarely  mention  any- 
thing regarding  that  a  change  of  rate  may  occur  owing  to  a  change 
of  temperature.  They  are  not  to  be  blamed  for  this,  for  the  rea- 
son that  if  many  seamen  were  to  receive  a  slip  mentioning  such  a 
thing  they  would  be  likely  to  ask  the  chronometer  man  why  he  could 
not  give  a  rate  good  for  all  climates. 

Still  if  they  would,  when  rating,  subject  the  chrenometer  to  an 
even  temperature  for  every  10°  above  normal  up  to  about  90°,  by 
placing  it  in  an  oven  or  incubator  for  a  few  days,  for  each  10°, 
and  then  note  on  the  slip  the  changes  in  the  rate,  the  master  could, 
if  he  watched  the  temperature,  get  a  much  better  result  from  his 
chronometers.  It  must  be  understood,  however,  that  the  tempera- 
ture meant  is  for  the  interior  of  the  case,  not  for  what  it  is  on 
deck,  for  there  may  be  quite  a  difference  between  it  and  the  deck 
temperature. 

Sending  Clironometers  Ashore. 

If  a  vessel  is  in  port  and  taking  on  board  a  cargo  where  the  ship 
would  be  subjected  to  severe  shocks  by  dropping  heavy  weights  on 
the  deck,  or  if  the  multifarious  duties  of  the  master  may  make  him 
forget  to  wind  as  regularly  as  at  sea,  or  if  a  steam  winch  is  situated 
directly  over  the  usual  place  for  keeping  the  chronometer,  it  is  cer- 
tainly advisable  that  it  should  be  sent  ashore  to  be  taken  care  of 
by  skillful  persons.  It  should  never  bo  intrusted  to  the  tender  mer- 
cies of  an  office  boy  if  left  in  the  owners'  or  agents'  office. 

As  a  final  word  of  caution,  do  not  trust  the  chronometer  to  any 
person  calling  himself  a  chronometer  maker  or  repairer,  unless  you 
have  first  satisfied  vourself  that  lie  is  a  reliable  man.  for  there  are 


Chroxometer.  305 


/ 


manv  watchmakers,  claiming  to  be  chronometer  makers  also,  who 
are  totally  unfit  to  perform  the  important  dut}'  of  rating,  cleaning 
and  even  of  takinsi"  care  of  a  chronometer. 

What  to  Do  if  the  Chroiiuiiietcr  Should  Break  Down. 

Kun  the  ship  to  the  latitude  of  your  destination  and  steer  to  the 
true  East  or  West,  as  the  case  may  be,  keeping  a  good  lookout,  as 
the  ship  will  be  running  on  dead  reckoning  longitude,  but  latitude 
by  observation. 

In  the  case  of  a  vessel  bound  to  a  United  States  port,  it  is  cer- 
tainly not  possible  to  miss  the  continent  of  North  America,  but  if 
bound  to  an  island  port  great  care  should  be  taken  to  discover  the 
position  of  the  snip  before  running  down  the  longitude,  as  she  may 
be  running  away  from  it  instead  of  towards  it. 

This  could  be  done  by  Lunars,  but  as  a  rule  vessels  whose  owners 
are  too  mean  to  provide  more  than  one  chronometer  have  rarely  a 
master  who  is  in  possession  of  the  requisite  knowledge  and  a  sex- 
tant fit  for  taking  such  observations,  and  as  Lunars  are  obsolete, 
owing  to  the  extreme  difficulty  in  obtaining  even  a  favorable  result, 
the  same  has  been  entirelv  omitted  from  this  work. 


Taylor's  Mod.   Nav.   20. 


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Taylor's  ^Ioderx  Xavigation. 


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DIVISION  XIV. 

THE   MARINER'S    COMPASS. 

This  instrument,  so  essential  in  tlie  practice  of  navigation,  is  of 
such  ancient  lineage,  that  its  origin  is  forever  buried  in  oblivion; 
still,  some  of  the  earlier  writers,  notably  the  'Jesuit  missionaries  to 
China,  have  proven  witliout  a  doubt  that,  in  a  crude  form,  it  was 
in  use  in  that  country  centuries  before  it  was  ever  lieard  of  in 
Europe. 

The  first  mention  of  its  use  in  Europe  was  by  a  merchant  travel- 
ing across  the  Mediterranean  Sea,  and  Mdien  writing  of  his  travels 
he  mentioned  the  fact  that  the  mariners  stuck  a  needle  in  a  eorn- 
husk,  then,  after  passing  over  it  a  lodestone,  placed  it  in  a  howl 
of  water;  it  was  then  found  to  indicate  the  North,  whereby  they 
were  enal)led  to  steer  their  craft  to  port. 

The  credit  of  attaching  the  needle  or  needles  to  a  card  has  been 
claimed  l)y  both  the  Italians  and  the  French;  but  it  is  safe  to  say 
that  the  modern  method  of  doing  it  is.  no  doubt,  considerably  dif- 
ferent from  the  first  attempt. 

It  is  not  the  intention  of  this  work  to  delve  too  deeply  into  the 
history  of  this  most  valuable  instrument;  so  we  will  here  leave 
that  part  to  tlie  professional  historian  and  proceed  with  the  essen- 
tials of  a  good  com]iass  and  other  matters  not  generally  known  to 
seamen. 

The  marking  of  the  card  is  of  the  first  and  primary  importance. 
This  should  be  done  to  degrees  and  very  accurately,  the  degrees 
commencing  at  0  for  North  and  South,  and  ending  at  90°  for  East 
and  West.  As  all  modern  navigators  always  calculate  to  degrees, 
it  would  be  a  verv  good  plan  if  the  old-fashioned  idea  of  "boxing 
the  compass"  in  points  were  done  away  with  entirely;  for  there 
have  been  many  mistakes  made  on  stormy  nights  when  giving  the 
course,  from  not  hearing  correctlv,  courses  having  been  steered  as 
many  as  four  points  in  eri'or.  in  mistaking  E.N.E.  for  E.S.E..  and 
so  on.  In  fact,  there  was  one  particular  case  that  came  under  the 
author's  notice  some  years  ago,  where  a  large  steamer  was  run 
ashore  in  the  vicinity  of  Rio  de  'Janeiro  for  this  reason. 

At  a  very  recent  date  the  United  States  Hydrograpliic  Office 
printed  a  form  of  compass-card  entirely  doing  away  with  ]ioints, 
and  at  the  time  asked  for  the  opinion  of  navigators  in  regard  to  it. 

It  is  to  be  regretted  that  it  received  very  little  of  the  attention 
it  deserved,  and   although  not  entirclv  approving,  as  the  change 


308  Taylor's  Modern  Xavigation. 

Avould  be  too  radical,  still  if  all  the  points  were  dispensed  with, 
excepting  X.S.E.  and  W.,  it  would  be  very  beneficial  to  the  naviga- 
tor. 

The  next  essential  is  to  have  a  properly  tempered  needle, — or 
needles,  I  should  say,  for  it  is  rarely  that  a  compass  is  seen  now- 
adays having  only  one.  The  shape  should  be  round,  never  flat. 
In  the  best  makes  of  compasses  there  are  as  many  as  eight  at- 
tached to  the  card.  This  gives  more  directive  power  and  causes 
the  compass  to  be  more  sensitive. 

When  attaching  the  needles  to  the  card,  great  care  should  be 
taken  that  the  line  of  force  is  exactly  parallel  to  the  North-and- 
South  line  of  the  card.  Any  error  in  this  respect  would  be  very 
dangerous,  as  observations  by  Amplitudes  or  Azimuths  to  deter- 
mine the  deviation  would  not  reveal  it. 

The  point  of  suspension  comes  next  in  order,  as  the  pivot  upon 
which  the  compass-card  rests  and  revolves  must  be  accurately 
centered  in  both  the  card  and  the  bowl.  It  should  be  understood 
that  on  the  under  side  of  the  card  is  a  cup  containing  an  agate, 
on  this  cup  the  card  rests  when  on  the  pivot.  The  point  of  this 
pivot  is,  or  should  be,  highly  polished,  so  that  when  the  card  is 
resting  upon  it  there  will  be  the  least  possible  friction.  Should 
there  be  a  flaw  in  the  agate,  it  will  eventually  dull  the  point  of  the 
pivot,  the  result  being  that  the  card  will  become  sluggish  or  appear 
to  stick,  requiring  to  be  frequently  shaken  up  to  make  it  move. 
If  such  a  thing  happens,  the  compass  should  be  sent  on  shore 
as  soon  as  possible  to  some  reputable  shop  for  repairs. 

Care  should  be  taken  to  prevent  the  edge  of  the  card  from 
touching  the  inside  of  the  bowl.  This  is  very  likely  to  occur 
if  the  pivot  has  not  been  properly  centered,  and  may  be  discovered 
by  turning  the  bowl  slowly  around  in  a  circle  and  watching  to  see 
if  at  any  time  the  card  follow  the  motion.  Although  the  card 
should  move  freely,  still  there  should  not  be  too  much  space,  for 
if  there  is,  the  helmsman  may  steer  as  much  as  one  quarter  of  a 
point  in  error,  if  he  is  steering  with  a  large  wheel  and  the  compass 
is  not  situated  directly  in  front  of  him. 

The  Luhher-Line  should  be  very  accurately  draM-n  in  tlie  bowl, 
and  should  be  placed  exactly  on  the  fore  ])art,  for  any  error  in 
these  respects  will  give  a  constant  amount  of  deviation,  dangerous 
because  hard  to  detect.  Tliis  will  be  more  elaborately  treated  as 
we  progress. 


C'oMi'Ass  Adjustment.  309 


I'urckimnij  a  Compass. 

Tn  purchasing  a  compass,  seamen  should  not  always  take  the 
word  of  the  maker  or  the  agent,  for  they  arc  not  always  competent 
judges,  as  the  following  incident  will  illustrate: 

It  was  the  writer's  fortune  once  to  he  employed  by  a  large  steam- 
ship company  for  the  purpose  of  compensating  compasi.'es  on  a  cer- 
tain vessel  recently  turned  over  to  them  by  the  builders.  On  going 
on  board  it  was  found  that  she  had  been  supplied  with  a  very  fine 
lot  of  binnacles, — fine  from  the  brass-finishers'  point  of  view, — 
which  proved  to  be  absolutely  valueless  in  directive  power  of  the 
compass-needles.  The  lubber-points,  also,  were  painted  on  the  in- 
side of  the  bowl  in  such  thick  lines  that  in  steering  it  was  possible 
to  steer  by  them  almost  half  a  point  in  error.  The  compasses  were 
rejected,  and  eventually  the  writer  had  a  visit  from  a  very  indig- 
nant maker  (  ?). 

In  course  of  conversation  I  asked  him  if  he  guaranteed  his  com- 
passes. He  answered  very  emphatically,  "Yes."  "For  how  long?" 
was  my  next  query,  and  his  answer  was,  "for  always." 

This  answer  alone  proved  that  the  man  did  not  have  the  slightest 
knowledge  of  the  first  principle  about  the  instrument  he  was  sup- 
posed to  manufacture;  for  it  is  common  knowledge  among  even 
the  uninitiated,  that  any  piece  of  steel  or  iron,  when  magnetized, 
will  eventually  lose  a  considerable  amount  of  its  power,  never  re- 
taining the  full  amount  of  its  original  strength,  the  tenacity  de- 
pending on  the  temper:  the  excess  of  what  it  can  hold  will 
leave  it,  eventually  reaching  at  what  is  generally  understood  as  a 
state  of  saturation,  and  even  afterwards  it  will  gradually  diminish 
in  strength  unless  it  is  kept  in  close  contact  with  another  body  of 
equal  power,  with  opposing  poles  together.  Take  for  instance  the 
horseshoe  magnet :  if  the  keeper  is  left  off,  it  will  gradually  lose  its 
power. 

The  best  magnets  in  the  world  to-day  are  made  under  the  super- 
vision of  Lord  Kelvin,  the  greatest  authority  on  such  matters  now 
living.    They  are  guaranteed  for  five  years  at  the  most. 

While  we  are  discussing  the  so-called  compass  makers  and  re- 
pairers it  may  not  be  amiss  to  give  another  instance: 

A  few  years  ago,  a  shipmaster,  an  old  friend,  telephoned  to  me 
to  come  down  to  his  ship  and  examine  the  compasses,  as  there  was 
something  radically  wrong.  Before  going  down  I  placed  in  my 
pocket  a  small  but  powerful  magnet,  which  I  generally  use  whrn 


310  Taylor's  Moderx  Xavigatiox. 

testing  a  compass  by  deflecting  the  needie.  Arriving  on  board,  I 
attempted  to  deflect  and  found  that  the  compass  barely  moved,  al- 
though the  magnet  was  held  so  as  to  touch  tlie  bowl.  I  informed 
the  master  that  there  was  something  very  much  the  matter  with 
the  card,  but  I  could  not  tell  without  opening  the  bowl.  The  mas- 
ter was  very  much  surprised,  as  it  had  been  in  the  hands  of  a 
"compass-repairer"  (  ?)   only  one  month  previously. 

I  insisted,  however,  in  opening  the  bowl  (it  was  a  liquid  com- 
pass), but  was  not  prepared  for  what  I  found,  viz.:  The  compass 
was  so  old,  and  the  tubes  containing  the  needles  having  leaked, 
there  was  not  one  piece  of  needle  one-half  inch  long,  they  were  so 
eaten  with  rust.  The  repairer  (God  save  the  mark!)  had  simply 
emptied  out  the  liquid,  gave  the  interior  a  clean  coat  of  paint,  re- 
filled the  bowl,  and  returned  it  to  the  master. 

Such  incidents  as  these  will  serve  to  show  that  the  master  cannot 
be  too  careful  to  whom  he  intrusts  the  vessel's  navigating  appli- 
ances when  needing  repairs. 

Parsimonious  Owners. 

It  is  not  an  uncommon  occurrence  for  masters  or  "cheese-par- 
ing" owners  to  perambulate  among  pawnshops  and  Junk-stores  and 
"pick  up"  an  ancient  compass  and  expect  the  vessel  to  be  navigated 
therewith.  To  this  kind  of  people  we  have  nothing  to  say,  for  we 
do  not  expect  for  one  minute  they  would  even  think  of  consulting 
a  book  of  this  kind,  so  let  them  go;  still,  to  the  honest  and  ambi- 
tious navigator,  we  certainly  hope  that  the  remarks  and  authentic 
incidents  here  related  will  be  of  some  benefit,  remembering  that 
some  compass-makers  may  Ije  excellent  mechanics  in  their  own 
particular  line  of  business,  but.  as  a  rule,  they  have  not  the  slight- 
est knowledge  of  the  practical  use  of  the  compass  at  sea,  and,  there- 
fore, they  are  not  competent  judges,  any  more  than  a  tool-maker, 
for  he  can  only  m'ake  tools,  and,  with  rare  exceptions,  cannot  use 
them. 

Tlie  liquid  compasses  iirc  very  much  in  favor  in  the  United 
States,  whereas  in  Europe  dry  compasses  are  mostly  used.  It  is 
hard  to  determine  which  is  the  better,  for  excellent  results  have 
been  had  with  both,  and  as  steadiness  of  the  card  at  se;!  is  the 
greatest  recommendation  for  the  liquid,  yet  if  the  card  is  con- 
structed on  the  Thompson  ])hui  of  extreme  liglitness.  and  corre- 
spondingly less  friction  witli  the  inininiutn  \v<Molit  at  tlie  edge  of 


Compass  Adjustment.  311 

card,  the  dry  compat^s  is  certainly  hard  to  beat.  Another  impor- 
tant point  in  favor  of  the  dry  card  is,  that  the  bowl  may  be  cleaned 
in  the  interior  by  any  careful  navigator,  whereas  with  a  liquid 
compass,  if  it  get  out  of  order,  such  as  air-bubbles  or  discoloration, 
it  must  be  sent  on  shore. 

Air-bubbles  are  caused  eitlier  from  the  bowl  not  having  been 
properly  filled  or  from  the  exposure  of  the  compass  to  a  hot  sun 
by  the  quartermaster's  leaving  the  top  olf.  Discoloration  of  the 
liquid  and  card  is  caused  by  the  chemical  action  of  the  liquid, 
which  is,  as  a  rule,  part  alcohol  and  part  distilled  water,  acting  on 
the  composition  or  paint  covering  the  interior  of  the  bowl. 

Caution  in  Regard  to  Placing  a  Compass,  and    Some    Incidents 
Eclating  to  the  Same. 

It  is  frequently  the  case  that  compasses  are  supplied,  placed,  and 
compensated  ready  for  sea,  as  the  builder  calls  it,  without  the  navi- 
gator or  shipmaster  having  the  slightest  thing  to  say  al)0ut  it. 
We  intend,  therefore,  in  this  article,  to  tell  some  very  plain  and 
forcible  home  truths  to  both  shipowners  and  shipmasters  regard- 
ing the  matter,  remembering  always  that  the  compass  is  the  most 
important  instrument  on  board  of  a  ship.  In  fact,  the  safety  of 
the  lives  on  board,  as  well  as  the  ship  itself,  is  centered  in  the  com- 
pass. 

By  paying  a  visit  to  some  of  our  coasting-vessels,  and  examining 
the  wheelhouses.  a  common  wooden  box  may  be  seen,  into  which  is 
dumped  another  box  containing  a  compass  of  some  kind  and  of 
doubtful  age.  This  box  is  generally  fixed  to  the  fore  part  of  the 
wheelhouse,  with  a  total  disregard  of  the  position  of  the  lubber- 
point.  And  not  only  this,  but  after  the  box  containing  the  compass 
is  placed  in  this  receptacle,  there  may  be  as  much  as  an  inch 
of  play  all  around.  This  is  generally  Avedged  up.  not  that  any 
attention  is  paid  to  the  lubber-point,  but  simply  to  keep  it  from 
sliding  around  in  the  box  when  the  ship  is  rolling.  Rxpert  navi- 
gators may  laugh  at  this,  as  an  exaggeration,  but  1  assure  them  it 
is  the  actual  truth,  and  not  an  exaggeration. 

The  master  of  one  of  these  vessels,  and  a  passenger  steam<M-  at 
that,  came  to  the  writer  one  day  and  asked  liis  opinion  as  to  why 
was  it  that  when  steering  to  the  Xorth  1k'  always  found  the  vessel 
too  far  inshore,  and  when  steering  Soutli,  too  far  offshore.  This 
master  had  been  navigating  his  vessel  with  tliese  results  for  over 


312  Taylor's  Modern  Navigation. 

a  year.  So,  scenting  a  badly  placed  lubber-point,  1  visited  his  ves- 
sel and  found  the  lubber-point  three-eighths  of  a  point  out  of  its 
proper  position.  This  was  not  the  builder's  fault,  as  the  master 
was  a  part  owner  and  had  superintended  the  building  of  the  vessel. 
Another  extremely  bad  case  of  placing  a  compass  was  detected 
by  the  author  on  board  of  the  steamer.  ,  .  .  This  valuable  iron 
ship  had  only  one  compass  in  position,  to  both  navigate  and 
steer  by. 

It  was  in  the  wheel-house,  on  a  table  built  of  common  lumber. 
eighteen  inches  forward  of  the  steering-wheel.  On  the  fore  part 
of  this  table,  right  under  the  compass  itself,  opened  a  regular 
bureau-drawer,  and  on  examination  this  drawer  was  found  to  con- 
tain a  sail-maker's  palm,  some  small  needles,  used  to  mend  flags 
and  some  pieces  of  bunting.  On  the  sides  of  the  compass  were  two 
square  boxes,  presumably  for  the  quadrantal  correction,  but  much 
loo  large,  which  when  opened  was  found  to  have  the  chain  con- 
tained in  it,  thrown  close  to  the  compass  on  one  side  by  the  ship's 
rolling  and  away  on  the  other.  (The  master  must  have  had  a 
lively  time  chasing  the  deviation  in  heavy  weather,  from  this 
cause  alone.)  The  stand  for  the  steering-wheel  was  next  opened, 
and  a  steel  rod  was  found  in  it,  the  top  part  being  within  eighteen 
inches  of  the  card  and  in  the  same  plane. 

It  was  the  request  of  the  master  that  this  compass  be  adjusted. 
Upon  being  denied  unless  the  needed  alterations  were  made,  he  be- 
came boisterous,  and  informed  the  adjuster  that  as  the  vessel  had 
run  on  it  so  long,  he  guessed  she  could  do  it  again. 

This  large  vessel  was  lost  not  long  afterwards,  the  same  master 
giving  as  an  excuse  an  unusual  set  of  a  mysterious  current.  I  have 
my  opinion,  however,  that  the  cause  was  something  different. 

It  is  a  very  bad  custom,  especially  on  board  of  American  ves- 
sels, to  have  lockers  directly  under  the  wheel-house,  into  which  are 
dumped,  when  not  in  use,  ropes,  blocks  with  iron  straps,  chain 
slings,  etc.,  with  a  delightful  and  happy-go-lucky  disregard  of  any 
untoward  effect  these  articles  might  have  on  the  compass. 

These  articles,  if  always  left  in  the  same  place,  would  not  be 
fraught  with  danger,  but  if  they  are  sometimes  on  one  side  and 
sometimes  on  the  other,  it  cannot  be  expected  that  the  sliip  will 
make  even  a  decent  course. 

Inspectors,  when  surveying  a  passenger-vessel,  should  insist  very 
emphatically  that  no  lockers  be  placed  in  or  under  the  wheel-house, 
in  wliicli  miulil  bc'  couccahMl  iron  or  steel  articles,  to  the  detriment 


Compass  AdjustiAiekt.  313 

of  the  compass;  and,  by  the  way,  it  is  just  as  well  to  mention  the 
fact  that  sometimes  the  pocket  of  the  helmsman  might  contain 
such  an  article  as  a  knife,  or  he  might  be  wearing  an  electric  belt; 
and  as  the  helmsman  stands  close  to  the  compass,  it  is  Just  as  well 
for  the  officer  of  the  watch  to  find  tliis  out,  or  a  wreck  may  occur. 

Bod  Position  to  be  Avoided. 

Some  vessels  have  the  bridge  arranged  so  badly  that  it  is  prac- 
tically impossible  to  compensate  the  large  natural  errors,  so  flTtit 
the  compass  may  be  depended  upon. 

A  case  in  point  was  that  of  an  iron  shij)  having  the  l)ridgc  in 
so  bad  a  position  that  the  standard  or  navigating  compass  was  only 
twelve  feet  from  the  smoke-stack,  and  between  the  compass  and 
the  smoke-stack  was  an  iron  ventilator,  or  air-shaft,  with  an  iron 
lid,  two  feet  square,  leading  down  to  the  fire-room.  The  lid  some- 
times was  lifted  up  and  at  other  times  was  shut  down.  This  com- 
pass was  flanked  on  both  sides  with  three  round  iron  ventilators 
with  movable  iron  cowls,  within  four  feet  of  the  compass-l^owl.  the 
railing  around  the  bridge  being  of  iron  also. 

The  compass,  which  was  of  the  best  make,  was  situated  directly 
over  the  wheel-house,  which  contained  the  steering-engine.  The 
space  between  the  engine  and  the  compass-card  was  exactly  six  feet. 
jSJ'ow,  who  but  a  person  willfully  obtuse  w'ould  ever  expect  that  a 
compass  in  such  a  position  could  be  depended  upon  to  keep  the 
same  error  for  two  consecutive  days?  Still,  the  adjuster  is  ex- 
pected, by  some  species  of  witchcraft,  to  "lick  it  into  shape."  This 
is  impossible.  He  may,  by  liberal  use  of  magnets,  reduce  the  errors 
to  manageable  limits,  but  if  the  errors  vary  afterwards,  the  poor 
adjuster  is  hauled  over  the  coals. 

The  proper  and  only  way  is  to  place  the  compass  in  such  a  posi- 
tion that  there  shall  not  l)e  any  iron  subject  to  alteration  in  its 
position  within  thirty  feet  of  the  compass.  This  could  be  done, 
if  it  were  not  for  the  managing  owner,  with  the  stockholder  at  his 
back,  hungry  for  dividends;  yet  it  is  mostly  the  master's  fault, 
for  if  he  have  the  courage  of  his  opinion,  and  insist  on  having  the 
compass  properly  placed  and  adjusted,  he  can  easily  gain  his  point, 
providing  he  is  not  himself  trying  to  gain  a  record  for  running  the 
vessel  cheaply. 

It  is  mistaken  economy,  anyway,  for  if  the  vessel  has  a  faulty 
compass,  a  straight  course  cannot  be  made,  with  loss  of  time.  etc.. 
as  a  consequence. 


314  Taylor's  Modern  Xavigatiox. 

Take,  for  instance,  a  steamship  with  a  faulty  compas;-.  and  >u\)- 
pose  that  through  it  the  vessel  loses  ten  miles  each  day.  lu  a  run 
of  thirty  da}'?  she  would  lose  three  hundred  miles.  Call  this  one 
good  day's  run.  Calculate  the  cost  of  fuel  for  one  day  and  add  to  it 
the  daily  expenses,  such  as  wages,  food,  and  insurance,  and  per- 
haps the  loss  of  a  tide,  and  it  will  be  seen  that  parsimony  in  regard 
to  compasses  and  other  navigating  appliances  is  a  bad  business 
proposition. 

The  engineer  of  a  steamship  needing  anything  for  his  depart- 
ment simply  makes  the  assertion  that  certain  supplies  or  repair- 
are  necessary,  and  they  are  immediately  supplied  to  him ;  but  if  the 
master  needs  anything  to  assist  him  in  the  safe  navigation  of  his 
vessel,  he  is  frowned  upon,  and  informed  that  Captain  So-and-so 
does  not  consider  it  a  necessity — why  should  he? 

The  master  is  supposed  to  supply  himself,  at  his  -^wn  expense, 
with  certain  instruments  to  enable  him  to  navigate  his  vessel ;  but 
it  has  never  been  required  of  the  engineer  that  he  should  provide 
tools  for  work  in  the  engine-room.     Why  make  the  difference  ? 

When  building  a  new  vessel,  the  master  or  compass-adjuster 
should  be  consulted  in  regard  to  the  arrangement  of  the  bridge  and 
the  fittings  in  the  vicinity  of  the  compasses.  This  is.  however, 
rarely  done,  the  engineer  or  constructor  having  full  control  of  such 
matters.  It  is  quite  correct  that  the  engineer  should  he  regarded  as 
the  most  competent  person  to  superintend  the  construction  of  the 
vessel's  hull  and  machinery,  but  he  is  certainly  not  a  competent  per- 
son so  far  as  the  bridge  is  concerned. 

As  before  remarked,  most  contracts  for  building  expressly  state 
that  the  vessel  shall  be  supplied  with  compasses  ready  for  sea,  the 
same  being  selected  by  a  person  connected  with  the  ship-l)uiUling 
firm,  called  a  buyer,  who,  as  a  rule,  has  not  the  slightest  knowledge 
about  the  essentials  of  a  good  compass.  It  is  actually  criniinal  ti> 
intrust  so  important  a  matter  to  such  a  notoriously  incompetent 
person.  In  the  author's  opinion,  such  matters  should  be  left  entirely 
to  the  discretion  of  the  master,  for  if  the  builder  supplies  the  com- 
passes, there  is  just  as  much  reason  that  he  should  supply  charts, 
sextants,  barometers,  thermometers,  and  chronometers,  for  they  are 
all  necessary  implements  required  in  navigating  a  ship. 

Kemember,  gentlemen,  that  there  is  an  old  saying,  'i']vi  ry  man  to 
his   trade. — the  shoemaker  to  his  last,  and  the  cook   to   the   fore- 


Compass  Adjist.mkxt.  315 


sheet."     Willi  ti'i<  paitiiiii- j-liot  we  will  now  itrocccd  witli  magnetism 
in  iron  ^Ili})s. 

:\IA(;XKTISM. 

Webster  deiines  magnetism  as  "tlu'  I'orei'  in  nature  wliieh  gives 
rise  to  the  plx'nomena  of  attraction,  polarity,  etc.,"  exhibited  by  the 
lodestone  and  otluM-  magnetic  bodies,  and  which  also  Jiad  l)een  de- 
scribed as  "that  l)ranch  of  physical  science  which  treats  of  the  na- 
ture and  properties  of  magnets  and  of  their  action  on  each  other.'' 

The  lodestone,  which  means,  in  English,  "to  lead,"  was  called  by 
Pliny,  "ferriim  viviim,"  or  quick  iron.  They  are  black  in  color,  and 
are  found  mostly  in  Asia  Minor.  They  were  considered  by  the 
ancients  to  have  magnetic  properties  I)ecause  of  their  pow'cr  in  at- 
tracting minute  particles  of  iron. 

Bars  or  elongated  masses  of  steel  or  iron,  when  charged  with 
magnetism  by  contact  or  friction  with  another  magnetic  body,  be- 
come what  are  known  as  artificial  magnets. 

The  earth  itself  is  a  large  natural  magnet,  the  ctfect  being  termed 
''terrestrial  magnetism,"  or  in  other  words,  the  magnetism  con- 
tained in  the  earth. 

Local  attraction  is  magnetism  contained  in  some  mass  other  than 
the  ship's  hull,  etc.,  but  which  is  sufficiently  near  to  the  ship  to  disturb 
the  compass-needle,  and  which  disappears  as  soon  as  the  ship  moves 
a  sufficient  distance  from  the  disturbing  mass. 

Permanent  magnetism  is  that  which  is  contained  in  a  ste(d  bar, 
having  in  itself  an  independent  power. 

Transient  magnetism  is  a  power  induced  into  a  mass  of  soft  iron 
by  having  an  independent  magnet  in  its  vicinity,  or  whicli  is  in- 
duced by  the  magnetism  of  the  earth.  It  is  not  stable,  liut  depends 
upon  the  position  of  the  disturbing  mass,  or  the  geographical  posi- 
tion. 

Subpcrmanent  magnetism  is  an  independent  force  acquired  by 
soft  iron,  but  which  is  subject  to  a  loss  of  power  in  tlie  lajise  of 
time. 

:\rAGXETl.SM  OF  THE  EARTH. 

If  the  reader  will  kindly  turn  to  tlie  defmitions  and  examine  the 
figure  representing  the  terrestrial  s]ihere,  it  will  be  noticed  that  the 


316  Taylor's  Modern  Navigation. 

magnetic  poles  are  not  at  the  same  place  as  the  true  poles,  bu!,  in- 
stead, are  situated  at  some  distance  from  them.  Now,  as  there  are 
magnetic  poles,  so  also  must  there  be  magnetic  meridians  and  a 
magnetic  equator.  This  will  go  to  show  that  there  are  two  ways  of 
looking  at  the  world,  viz.,  one  in  its  true  character  and  the  other  iu 
its  magnetic  character ;  and  let  it  be  remembered  that  it  is  the  lat- 
ter which  will  be  referred  to  throughout  this  section. 

The  magnetic  pole  is  that  pole  towards  which  the  compass-needle 
points  when  not  affected  by  iron  in  its  vicinity. 

Magnetic  meridians  are  great  circles  passing  from  the  magnetic 
North  Pole  to  the  magnetic"  South.  Pole.  The  compass-needle  will 
always  lie  along  one  of  these  when  it  is  free  from  deviation.  If 
the  needle  deviates  from  it,  the  resulting  angle  will  l)e  the  devia- 
tion. 

The  magnetic  equator  is  a  circle  passing  around  the  earth,  about 
half-way  between  the  magnetic  Poles,  and  really  means  that  if  a 
magnetic  needle  is  freely  suspended  so  that  it  will  move  vertically, 
it  will  hang  perfectly  horizontal  as  long  as  it  is  on  the  magnetic 
equator,  but  should  the  needle  be  taken  to  any  other  part  of  the 
world,  it  wall  leave  its  horizontal  position  and  one  end  will  dip. 

Dip  or  inclination  of  the  magnetic  needle  is  tlie  angle  between 
the  position  of  the  needle  and  a  horizontal  plane.  A  line  drawn 
through  the  needle  itself  would  represent  a  line  of  force.  This 
dipping  of  the  needle  is  caused  by  its  pointing  towards  the  magnetic 
pole  through  earth,  instead  of  towards  the  North  point  of  the 
horizon.  It  is  of  the  utmost  importance  that  this  definition  be 
thoroughly  understood,  as  the  dip  of  the  locality  where  the  ship 
was  built  has  a  considerable  influence  on  the  magnetic  character  of 
the  ship. 

The  dip  on  the  magnetic  equator  is  zero,  as  the  needle  hangs  hor- 
izontally. At  either  the  magnetic  North  or  the  magnetic  South 
Poles  the  needle  would  be  vertical,  or  would  have  a  dip  of  90°.  It 
must  not  be  assumed  that  it  jumps  to  this  dip  all  of  a  sudden,  for 
such  is  not  the  case,  as  it  gradually  changes  from  the  horizontal  and 
assumes  the  vertical  as  the  ship  leaves  t\\o  iiiagiietic  ciiiiator  and 
approaches  the  magnetic  poles.  Charts  of  the  di])  I'oi'  the  whole 
world  are  published  each  year  by  the  Tnited  States  government, 
tlie  magnetic  dip  for  any  place  may  1h'  determined  by  simj)ly  re- 
ferrini,'-  to  these  charts. 


CoiiPASs  Adjustment.  317 

Chance  for  Argument. 

It  is  popularly  supposed  that  the  North  end  of  the  compass-needle 
points  towards  the  North.  This  supposition  is  incorrect ;  therefore, 
it  is  necessary  that  the  student  should  be  disabused  of  this  idea  be- 
fore he  advances  much  further,  or  he  is  likely  to  become  very  much 
entangled.    To  prove  this  we  will  give  the 

First  Law  of  Magnetism,  Wliicli  is. 

Opposite  properties  attract; 

Similar  properties  repel. 

If  this  is  so,  then  the  North  end  of  a  compass-needle  could  not 
point  North, — in  fact,  it  must  point  South.  This  is  very  confusing, 
because  by  this  law  a  North  will  repel  a  North,  and  a  South  will 
repel  a  South,  but  a  North  will  attract  a  South,  and  vice  versa. 

The  only  safe  way  is  to  speak  of  that  end  of  the  compass-needle 
that  points  towards  the  North  as  the  North-seeking  end,  and  al- 
though many  modern  writers  have  given  various  names  to  the  poles 
according  to  their  own  ideas,  in  this  work  Airy's  method  of  color 
will  be  used,  as  it  quickly  catches  the  eye,  and  serves  the  purpose 
of  illustration  better  than  any  other  method. 

Eed  will  therefore  always  be  understood  as  meaning  the  North- 
seeking  end,  and  Blue  as  meaning  the  South-seeking  end  of  a  mag- 
net. The  student  will  then  see  at  a  glance  the  "first  law  of  mag- 
netism," as  same  colors  placed  together  will  repel,  but  contrary 
colors  will  attract. 

MAGNETISM   IN   AN   IRON'    SHIP. 

Before  taking  up  the  all-important  study  of  conn)ass-a(ljustment 
it  will  be  necessary  for  the  student  to  thoroughly  understand  the 
distribution  of  the  magnetism  in  the  hull,  beams,  masts,  and  fun- 
nels of  an  iron  ship,  to  analyze  the  causes  and  sort  them  out.  so  to 
speak,  so  that  when  compensating  the  errors  of  the  compass  pro- 
duced thereby,  it  may  l)e  done  in  an  intelligent  and  practical  nnui- 
ner,  for  without  a  thorough  knowledge  of  the  causes,  no  one  can 
expect  to  be  a  successful  compass-adjuster. 

A  ship  built  of  iron  should  be  considered  in  the  light  of  a  very 
large  magnet.  She  is  so  in  fact,  for  she  acquired  magnetism  while 
underffoinof  construction,  bv  tlu-  hammerino-  and  rivetinsc  of  the  ribs 


318  Taylor's  MoDEitx  Navigation. 

and  plates  when  fitted  together  until  they  became  a  more  or  less 
elongated  mass  capable  of  receiving  and  retaining  a  certain  amount 
of  polarity. 

This  magnetism,  so  induced  into  the  hull,  is  termed  Subperma- 
nent,  the  position  of  the  poles  in  the  ship  depending  on  the  direction 
of  the  ship's  head  while  on  the  stocks  and  on  the  magnetic  dip  of 
the  locality  wliere  the  ship  was  built.  It  should  not  be  understood 
that  the  ship  will  retain  all  the  magnetism  so  acquired,  for  such  is 
not  the  case;  in  fact,  there  will  be  a  very  rapid  change  in  the  amount 
after  the  ship  leaves  the  stocks  until  the  iron  in  the  ship's  hull 
reaches  the  saturation-point,  when  it  will  remain  practically  con- 
slant  for  all  time  and  places,  unless  the  construction  of  the  hull  is 
altered. 

If  the  ship's  head  was  placed,  after  the  launching,  in  an  opposite 
direction  from  that  pointed  to  when  she  was  being  built,  a  large 
amount  of  the  magnetism  induced  by  the  hamuiering,  etc..  would 
be  hammered  out  of  her  again ;  therefore,  it  would  be  a  good  plan 
if  the  owners  of  the  vessel  insisted  on  this  being  done,  when  specifi- 
cations are  submitted  to  them  for  approval.  The  reason  is  obvious, 
for  as  the  Subpernianent  magnetism  changes  so  rapidly  after  the 
launching,  any  compass  adjusted  before  the  hull  reaches  the  satura- 
tion-point will  not  remain  in  the  same  for  even  one  day ;  and  al- 
though the  matter  of  completing  the  ship  with  her  head  in  an  op- 
posite direction  may  not  entirely  do  away  with  the  excess  of  the 
Subpermanent  magnetism,  it  certainly  will  assist  in  materially  de- 
cj-easing  it,  with  the  result  that  the  compass  will  not  &how  such  an  ex- 
tremely variable  error.  It  may  not  be  possil)le  always  to  do  as  above 
advised,  owing,  perhaps,  to  the  peculiar  location  of  the  ship-yard 
or  its  wharves;  still,  the  master,  before  taking  the  ship  to  sea,  should 
insist,  as  far  as  practicable,  that  the  ship  be  anchored  for  a  few 
days  in  such  a  position  that  the  direction  of  her  head  will  be  sub- 
jected to  alternation  by  the  change  of  the  tides.  If  these  instructions 
are  not  carried  out.  any  adjustment  made  or  deviation  ascertained 
will  not  be  worth  the  scratch  of  a  pencil. 

Vessels  built  of  hard  iron  or  of  steel  receive  nmgnclisui  slowly. 
and  are  correspondingly  more  retentive,  and  will  take  a  much 
k.nger  time  to  get  rid  of  the  excess  of  the  Subpermanent  magnet- 
ism; therefore,  with  a  vessel  built  of  steel,  it  is  more  imperative  to 
alter  the  direction  of  her  head  than  with  a  vessel  built  of  com- 
paratively soft  iron. 

Subpermanent  uiagnetisni  ])roduc<'s  semicircular  deviation, 
which  means  that  Easterlv  dcvialion  will  be  found  on  one-half  of 


CojLPAss  Adjustment.  319 


the  compass,  and  Westerly  deviation  will  be  i'ound  on  the  other 
half,  with  the  point  of  no  deviation  diametricalk  ojjposed ;  that  i<, 
if  thcM'c  is  ni>  deviation  on  Xorth  there  will  he  none  on  South. 
There  will  also  be  two  points  diametrically  o])pose(l  where  it  is 
greatest;  but  the  names  of  the  deviation  will  be  opposite;  that  is, 
if  20°  E.  is  found  on  West,  then  20°  W.  will  be  found  on  l^ast. 
The  student  should  bear  in  mind  that  he  will  not  always  find  tlii.- 
actually  shown  by  a  compass  unless  he  eom])utes  the  coetheient, 
which  will  be  explained  further  on. 

Transient  magnetism  in  a  ship  is  contained  in  all  iron  that  is 
vertical,  such  as  iron  masts,  funnels,  ventilators,  davits,  stanchions, 
etc. 

All  vertical  iron,  no  matter  whether  it  is  on  board  of  a  ship  or 
on  shore,  becomes  magnetized  by  induction  of  the  earth's  magnetic 
force;  the  disturbing  effect  it  has  on  a  compass-needle  depending 
on  the  dip  of  the  locality. 

The  lower  end  of  a  bar  of  vertical  iron  always  takes  on  the  char- 
acter of  the  pole  that  is  nearest  to  it,  and  the  upper  end  the  opposite 
character.  Therefore,  in  North  magnetic  latitude  the  lower  end 
will  always  be  North,  or  red,  and  will,  therefore,  push  the  North 
or  red  end  of  a  compass-needle  away.  Consequently,  the  upper  end 
will  be  South,  or  blue,  and  will  attract  the  Xorth  or  red  end  of  a 
compass-needle. 

The  reverse  will  be  the  effect  for  a  South  latitude. 

A  bar  of  iron  held  vertically  over  the  magnetic  equator  would 
not  have  the  slightest  effect  on  any  compass  in  its  vicinity,  for  the 
reason  that  the  induction  of  or  by  the  magnetic  poles  is  neutralized 
by  the  iron  being  equidistant  from  both;  but  if  the  bar  is  taken 
from  the  magnetic  equator  towards  either  one  of  the  magnetic  polos, 
it  immediately  becomes  magnetized.  If  the  bar  is  held  vertically 
over  the  North  magnetic  pole  it  will  then  receive,  by  induction,  the 
full  effect  of  the  earth's  magnetic  force,  the  lower  being  red  of 
great  intensity,  and  the  upper  blue. 

This  changing  of  the  magnetic  intensity  found  in  vertical  iron 
is  one  of  the  principal  causes  of  the  great  alternation  in  the  deviation 
of  the  compass  as  the  ship  shifts  her  position  on  the  surface  of  the 
earth,  and.  as  no  doubt  will  l)e  seen  by  this  time,  the  disturbing 
power  depends  on  the  magnetic  dip  of  the  locality  where  the  ship 
happens  to  be. 


320  Taylor's  Modern  Xavigatiox. 

Transient  magnetism  foimd  in  vertical  iron  produces,  als'O,  semi- 
circular deviation,  as  previously  described;  but  as  the  causes  are 
totally  different,  and  as  the  one  is  practically  constant  for  all  lat- 
itudes, while  the  other  is  constantly  changing,  the  method  of  com- 
pensation cannot  be  the  same.    This  will  eventually  be  explained. 

Magnetism  Contained  in  Iron  Lying  Horizontal,  Such  as  the  Beams 
and  BuR-heads  of  an  Iron  Ship. 

As  already  explained,  the  magnetism  in  the  ship's  hull  (Subper- 
manent)  and  vertical  iron  (Transient)  both  produce  semicircular 
deviation  and  from  different  causes;  but  the  deviation  caused  by 
horizontal  iron  is  produced  by  a  totally  different  law,  viz.,  horizontal 
induction,  the  result  being  termed  Quadrantal  Deviation,  which  is 
so  named  because  it  is  greatest  at  the  quadrantal  points,  X.E.,  S.E., 
S.W.,  and  X.W.,  but  is  zero  at  the  cardinal  points,  X.,  S.,  E.,  and 
W. 

To  demonstrate  the  effect  of  horizontal  iron,  the  student  is  ad- 
vised to  test  by  experiment  with  any  compass  what  is  here  asserted. 

If  a  bar  of  soft  iron  is  held  so  that  it  is  in  a  direct  line  wffch  a 
compass-needle,  but  with  one  end  near  the  Xorth.  it  will  be  found 
tbat  it  will  have  no  disturbing  effect  on  the  compass-needle;  but  if 
it  is  moved  so  that  it  will  make  an  angle  of  not  greater  than  90°, 
the  bar  pointing  directly  to  the  center,  it  will  immediately  attract 
the  Xorth,  having  the  greatest  disturbing  effect  when  the  angle  is 
45°. 

If  the  bar  is  held  at  right  angles  to  the  compass-needle,  with  the 
end  pointing  towards  the  center,  it  will  have  no  effect. 

If  it  is  held  in  a  direct  line  with  the  needle,  but  with  the  end 
near  the  South,  there  will  be  no  disturbance;  but  if  held  at  any 
other  angle  except  90°,  the  South  will  be  attracted  to  it,  the  great- 
est effect  being  when  the  bar  is  pointing  towards  the  center  of  the 
compass  at  an  angle  of  45°  with  the  compass-needle. 

Tlierei'ore,  the  law  of  disturbance,  as  illustrated,  is.  that  a  T)ar 
of  horizontal  soft  iron  will  attract  that  end  of  the  coni])ass-nee(lle 
that  is  nearest  to  it;  the  result  being,  (hat  luu'izontal  iron  has  the 
least  effect  when  it  is  lying  in  the  sanu'  line  of  force  as  the  needle, 
parallel  to  it  or  at  right  angles  with  it,  hul  has  its  greatest  "effect 
when  I  he  mass  is  at  an  angle  of  45°  with  the  compass-needle.     It 


FIG.  5    ^\^^  flips   Head 


NORTH 


e/  3TARB0/1RD  side      X  N 


FIG.  4 


(Sljips  Head 

SOUTH 


ur 


PORT   SIDE 

E  N 


FIG.  5 


Compass  Adjustment.  321 

will,  therefore,  be  seen,  that  as  the  direction  of  the  ship's  head  al- 
ters, so  also  must  the  angle  between  the  needle  and  the  horizontal 
iron,  causing  a  change  in  the  deviation. 

EXPLANATIOX  OF  COLORED  DIAGEAMS. 
Fig.  3,  Ship's  Head  North  in  North  Latitude. 

This  illustration  shows  the  Subpermanent  magnetism  contained 
in  an  iron  vessel  owing  to  her  head  being  North  while  building. 
The  arrow  S.jST.,  represents  the  dip  of  the  locality,  and  the 
line  EE,  at  right  angles  to  it,  represents  the  equator  of  the  dip. 

A  vessel  built  under  such  conditions  will  have  red  or  Xorth  mag- 
netism in  her  fore  foot,  and  blue  or  South  magnetism  in  the  upper 
part  of  her  stern,  with  the  greatest  intensity  in  those  places,  but 
which  gradually  diminish  towards  the  equatorial  line,  as  illustrated 
by  the  intensity  of  coloring. 

That  part  of  the  deck  which  the  line  EE  passes  through  is 
neutral,  and  a  compass  placed  in  such  a  position  would  not  be 
affected  by  Subpermanent  magnetism,  as  it  would  practically  be 
equidistant  from  the  poles  of  the  ship,  but  if  it  were  placed  on  any 
other  part  of  the  deck,  it  would  be  immediately  affected. 

The  line  of  force  in  the  ship  being  fore  and  aft,  and  the  compass- 
needle  lying  in  the  same  direction,  namely,  fore  and  aft,  also,  or 
in  other  words,  if  the  ship  is  heading  North  or  South  by  compass, 
there  will  be  no  deflection  of  the  needle,  but  if  the  North  or  red  end 
of  the  needle  should  point  to  the  North  or  red  end  of  ship,  and  the 
South  or  blue  end  of  the  needle  should  point  to  the  South  end  of 
ship,  the  compass  will  be  sluggish,  but  if  the  blue  end  of  the  needle 
points  to  the  red  end  of  the  ship,  then  the  needle  will  be  sensitive. 

If  the  needle  leaves  the  ship's  line  of  force,  it  will  be  immediate- 
ly disturbed,  especially  by  the  stern,  as  there  is  more  blue  on  deck 
aft  than  there  is  red  forward,  the  North  end  of  the  needle  being  at- 
tracted towards  the  stern  will  cause  the  maximum  amount  of  dis- 
turbance when  the  ship  is  heading  East  or  West,  or  when  the  needle 
is  at  right  angles  to  the  line  of  force  in  the  ship. 

Fig.  2,  Ship's  Head  West. 

This  illustration  shows  the  stern  of  the  ship  and  the  Subperma- 
Jient  magnetism,  owing  to  her  being  built  with  her  head  "West. 


322  Taylor's  Modern  Navigation. 

In  this  case  the  lower  part  of  the  starboard  side  will  be  red,  viz., 
that  part  below  EE,  and  the  upper  part  of  the  port  side  will  be  blue, 
with  great  intensity,  the  port  side  of  the  ship  having  greater  effect 
than  the  starboard  side,  owing  to  the  blue  pole  of  the  ship  being 
nearer  to  a  compass  situated  on  the  deck.  The  result  will  be  that 
if  the  ship  is  heading  on  an  East  or  a  West  course  the  neeedle  will 
lie  athwartships,  and  in  the  ship's  line  of  force.  In  such  a  case 
there  will  be  no  deflection  of  the  needle,  and  therefore  no  deviation ; 
but  if  the  ship  is  heading  so  as  to  bring  the  North  or  red  end  of  the 
compass-needle  to  the  blue  side  of  the  ship,  then  it  will  be  sensitive, 
but  if  the  blue  end  of  the  needle  is  directed  to  the  blue  side  of  the 
ship,  it  will  be  sluggish.  The  greatest  effect  on  the  compass-needle 
will  be  found  when  the  needle  is  fore  and  aft,  as  it  would  be  at  right 
angles  to  the  line  of  force  in  the  ship,  the  needle  being  attracted 
strongest  to  the  port  side. 

Fig.  1,  Ship's  Head  East,  Bow  View. 

This  illustration  shows  the  Subpermanent  magnetism  in  a  §'hip 
with  her  head  east  while  building. 

The  port  bilge  having  been  nearest  to  the  North,  is  therefore  red, 
and  the  upper  part  of  the  starboard  side  is  blue,  owing  to  its  having 
been  farthest  from  the  North  while  building.  The  effect  on  a  com- 
pass will  be  that  the  red  end  of  the  needle  will  be  attracted  to  the 
starboard  side. 

Fig.  Jf,  Ship's  Head  South,  Showing  Port  Side. 

This  illustration  shows  the  effect  on  a  ship  with  her  head  South 
while  building. 

In  this  case  the  most  power  is  in  the  upper  part  of  the  bow,  and 
is  blue,  because  it  was  the  part  of  the  ship  farthest  from  the  North 
while  building.  The  greatest  intensity  of  red  magnetism  will  be  in 
the  lower  part  of  the  stern.  This  is  the  contrary  case  to  that  of 
ship's  head  north  while  building. 

Fig.  5,  Ship's  Head  North  and  Vertical  Iron. 

The  hull  of  ship  in  this  case  will  have  the  same  coloring  of  Sub- 
permanent  magnetism  as  that  in  Figure  3,  but  with  the  port  side 
towards  the  reader,  so  it  needs  no  further  explanation,  but  the 


322  Taylor's  Modern  Navigation. 

In  this  case  the  lower  part  of  the  starboard  side  will  be  red,  viz., 
that  part  below  EE,  and  the  upper  part  of  the  port  side  will  be  blue, 
with  great  intensity,  the  port  side  of  the  ship  having  greater  effect 
than  t'he  starboard  side,  owing  to  the  blue  pole  of  the  ship  being 
nearer  to  a  compass  situated  on  the  deck.  The  result  will  be  that 
if  the  ship  is  heading  on  an  East  or  a  West  course  the  neeedle  will 
lie  athwartships,  and  in  the  ship's  line  of  force.  In  such  a  case 
there  will  be  no  deflection  of  the  needle,  and  therefore  no  deviation ; 
but  if  the  ship  is  heading  so  as  to  bring  the  North  or  red  end  of  the 
compass-needle  to  the  blue  side  of  the  ship,  then  it  will  be  sensitive, 
but  if  the  blue  end  of  the  needle  is  directed  to  the  blue  side  of  the 
ship,  it  will  be  sluggish.  The  greatest  effect  on  the  compass-needle 
will  be  found  when  the  needle  is  fore  and  aft,  as  it  would  be  at  right 
angles  to  the  line  of  force  in  the  ship,  the  needle  being  attracted 
strongest  to  the  port  side. 

Fig.  1,  Ship's  Head  East,  Bow  View. 

This  illustration  shows  the  Subpermanent  magnetism  in  a  ship 
with  her  head  east  while  building. 

The  port  bilge  having  been  nearest  to  the  North,  is  therefore  red, 
and  the  upper  part  of  the  starboard  side  is  blue,  owing  to  its  having 
been  farthest  from  the  North  while  building.  The  effect  on  a  com- 
pass will  be  that  the  red  end  of  the  needle  will  be  attracted  to  the 
starboard  side. 

Fig.  Jf,  Ship's  Head  South,  Showing  Port  Side. 

This  illustration  shows  the  effect  on  a  ship  with  her  head  South 
while  building. 

In  this  case  the  most  power  is  in  the  upper  part  of  the  bow,  and 
is  blue,  because  it  was  the  part  of  the  ship  farthest  from  the  North 
while  building.  The  greatest  intensity  of  red  magnetism  will  be  in 
the  lower  part  of  the  stern.  This  is  the  contrary  case  to  that  of 
ship's  head  north  while  building. 

Fig.  5,  Ship's  Head  North  and  Vertical  Iron. 

The  hull  of  ship  in  this  case  will  have  the  same  coloring  of  Sub- 
permanent  magnetism  as  that  in  Figure  3,  but  with  the  port  side 
towards  the  reader,  so  it  needs  no  further  explanation,  but  the 


< 

m 


Compass  Adjustment.  323 

smoke-stack  is  to  represent  the  transient  magnetism  found  in  vertical 
iron.  This  case  is  for  North  magnetic  latitude,  therefore  the  lower 
part  of  the  stack  being  nearest  to  the  North  magnetic  pole,  it  must 
take  on  the  character  of  that  pole,  so  it  is  colored  red,  while  the 
upper  part,  being  farthest  away,  must  take  on  the  contrary  charac- 
ter, and  is  therefore  blue.  The  effect  on  a  compass  would  be  that 
of  attracting  more  strongly  the  North  end  of  the  needle  towards  the 
stern,  that  is  if  the  compass  is  placed  on  the  fore  part  of  the  funnel 
and  elevated  above  the  deck,  as  both  the  top  part  of  funnel  and  stern 
of  ship  have  blue  magnetism.  Should,  however,  the  compass  be 
placed  on  the  deck  near  the  lower  end  of  smoke-stack,  then  the  North 
end  of  the  needle  would  be  repelled  thereby,  the  amount  of  the  re- 
pelling force  depending  on  the  mass.  This  idea  of  placing  the  verti- 
cal iron,  or  smoke-stack,  with  the  hull,  is  to  serve  the  purpose  of 
illustration,  but  be  it  remembered  that  the  magnetism  in  the  hull, 
called  Subpermanent,  is  practically  the  same  for  all  latitudes,  where- 
as the  magnetism  in  the  vertical  iron  depends  upon  the  magnetic 
latitude  of  the  ship  or  dip  of  locality. 

Fig.  6,  Ship's  Head  N.E.,  Dech  Plan. 

This  illustration  shows  the  deck  plan  of  a  ship  with  her  head 
N.E.  while  building. 

It  will  be  seen,  in  this  case,  that  the  port  bow  was  nearest  to  the' 
North  while  building,  and  is  therefore  red,  and  the  starboard  quar- 
ter farthest  from  North,  and  is  therefore  blue. 

The  effect  on  a  compass  will  be,  if  the  ship  is  heading  in  a  direc- 
tion the  same  as  or  opposite  to  that  of  her  head  when  being  built, 
there  will  be  no  deviation,  because  the  needle  would  be  lying  in  the 
ship's  line  of  force. 

This  is  a  combination  of  that  of  a  ship's  head  built  North  or 
East,  as  the  red  is  found  partly  in  the  bow  and  partly  in  the  port 
side,  and  the  blue  is  partly  in  the  stern  and  partly  in  the  starboard 
quarter.  The  maximum  effect  on  the  compass-needle  will  be  when 
the  ship  is  heading  N.W.  or  S.E.,  because  at  those  times  the  needle 
will  be  at  right  angles  to  the  ship's  line  of  force,  the  North  or  red 
end  of  the  needle  being  attracted  towards  the  stern  and  the  star- 
board quarter. 

Fig.  7,  Shifs  Head  S.W.,  Deck  Plan. 

This  illustration  shows  the  deck  plan  of  a  vessel  built  with  her 
head  S.W.     It  is  the  contrary  case  to  that  of  a  ship  built  with  her 


32-i  Taylor's  Mouerx  Xavigatiox. 

head  X.E.  Here  the  South  or  blue  magnetism  is  found  in  the  port 
bow  and  the  red  in  the  starboard  quarter.  The  efEect  here  will  be 
no  deviation  when  ship  is  heading  S.W.  or  X.E.,  but  the  greatest 
efEect  will  be  when  the  ship  is  heading  on  X.W.  or  S.E.,  as  at  such 
times  the  needle  will  be  at  right  angles  to  the  ship's  line  of  force. 
the  North  end  of  the  needle  being  attracted  to  the  bow  and  the  port 
side  of  the  ship. 

Fig.  8,  Ship's  Head  East,  Deck  Plan. 

This  illustration  shows  the  magnetic  character  of  a  ship  built 
with  her  head  East. 

In  this  case  the  subpermanent  magnetism  will  lie  in  the  sides 
of  the  ship,  and  none  in  the  ends  of  the  ship.  The  preponderance 
of  power  will  be  in  favor  of  the  blue,  as  its  intensity  is  in  the  upper 
part  of  the  starboard  side,  and  correspondingly  nearer  to  a  compass 
situated  on  the  deck,  whereas  the  red  will  be  in  the  lower  part  of  the 
port  side  or  bilges.  The  effect  on  a  compass  will  be  that  of  attract- 
ing the  Xorth  end  of  the  needle  to  the  starboard  side,  with  no  fore- 
and-aft  attraction  whatever. 

Fig.  11,  Ship's  Head  S.E.,  Deck  Plan. 

This  is  a  contrary  case  to  that  of  a  ship  built  with  her  head  X.W.. 
with  the  points  of  no  deviation  the  same  and  the  points  of  maxi- 
mum deviation  also  the  same,  but  with  blue  magnetism  in  the  star- 
board bow  and  red  in  the, port  quarter.  In  this  case  the  needle  will 
be  attracted  towards  the  fore  part  of  the  ship  and  the  starboard 
side. 

Fig.  9,  Sliip's  Head  N.W..  Deck  Plan. 

This  illustration  shows  the  magnetic  condition  of  a  ship  built 
with  her  head  X.W. 

In  this  case  the  starboard  bow  will  have  red  magnetism  and  the 
port  quarter  blue,  the  effect  here  being  that  on  X.W.  and  S.E. 
courses  the  needle  will  lie  in  the  ship's  line  of  force,  and  therefore 
will  have  no  deviation,  whereas  on  N.E.  or  S.W.  courses  the  maxi- 
mum effect  will  be  felt,  a,&  the  needle  would  be  at  right  angles  to 
the  ship's  line  of  force. 

Here  the  North  end  of  the  needle  is  attracted  partly  to  the  port 
quarter  and  partly  towards  the  stern. 


> 

2 


So 


Compass  Adjustment,       •  '  i'  325 


Fig.  10,  Ship's  Head  West,  Deck  Plan. 

This  illustration  is  a  contrary  case  to  that  of  a  ship  built  with 
her  head  East.  There  is  no  fore-and-aft  attraction,  but  all 
athwartship  attraction,  the  needle  being  attracted  to  the  port  side. 

The  points  of  no  deviation  would  be  East  and  West  and  maxi- 
mum at  Xorth  and  South. 

Innumerable  diagrams  could  be  given,  showing  the  subperma- 
nent  magnetism  for  other  directions  of  ship's  head  while  building, 
but  the  author  feels  assured  that  those  that  have  been  given  will 
be  sufficient  to  illustrate  the  subpermanent  character  of  ship.  From 
these  diagrams  it  will  be  seen  that  the  North  end  of  the  compass- 
needle  is  drawn  to  or  repelled  from  different  parts  of  the  ship,  and 
the  reason  why.  The  student  will  also  see,  by  this  time,  that  the 
compa&'s-needle  may  be  disturbed  by  different  parts  of  the  ship, 
not  only  by  the  hull,  but  also  by  vertical  iron,  both  of  these  pro- 
ducing semicircular  deviation,  but,  as  before  remarked,  the  effect 
of  the  subpermanent  is  practically  constant,  whereas  the  effect  of 
the  transient  magnetism  is  vertical  iron  continually  varies,  accord- 
ing to  the  dip  of  the  locality.  There  is  also  another  disturbing 
power  to  be  taken  into  consideration,  namely,  that  contained  in 
horizontal  iron.  The  effect  is  totally  distinct  from  the  others.  This 
we  will  treat  of  when  we  finish  wdth  the  semicircular  deviation. 

SORTING  OUT  THE  DEVIATIOX. 

This  is  done  by  giving  a  name  to  each  disturbing  power,  accord- 
ing to  which  part  of  the  ship  the  N^orth  end  of  needle  is  at- 
tracted. These  forces  are  designated  by  the  letters  A,  B,  C,  D,  and 
E,  and  are  called  coefficients. 

Coefficient  A  represents  an  effect  on  the  compass  that  is  constant 
for  all  directions  of  the  ship's  head.  It  may  be  caused  by  a  poorly 
constructed  card,  the  needle  not  being  parallel  to  the  jSTorth  and 
South  line,  unequal  distribution  of  iron  in  the  vicinity  of  the  com- 
pass or  a  lubber-line  wrongly  placed.  A,  as  a  rule,  is  very  small, 
or,  at  least,  it  should  be ;  if  not,  the  card  and  lubber-line  should  be 
examined. 

The  coefficients  B  and  C  represent  the  semicircular  deviation, 
or,  in  other  words,  the  amount  of  deviation  produced  by  both  the 
subpermanent  magnetism  in  vessel's  hull  and  the  transient  mag- 
netism in  vertical  iron. 


326  Taylor's  Modern  Navigation. 

Coefficient  B  represents  a  force  acting  fore  and  aft,  such  as  would 
occur  in  a  vessel  built  with  her  head  North  or  South. 

—  (minus)  B  when  the  Xorth  end  of  the  needle  is  drawn  to- 
ward the  stern,  and  +  (pl^^s)  B  when  drawn  towards  the  bow. 

Coefficient  C  represents  a  force  acting  athwartship,-[-C  when 
North  end  of  needle  is  drawn  towards  the  starboard  side,  and  — C 
when,  drawn  to  port  side. 

The  value  of  the  coefficients  depending  to  a  great  extent  on  the 
direction  of  the  ship's  head  while  building. 

Take,  for  instance,  the  colored  figure  of  a  ship  built  with  her 
head  North.  Here  the  attraction  would  be  all  fore-and-aft,  and 
none  athwartship.  In  such  a  case  the  North  end  of  the  needle 
would  be  attracted  towards  the  stern ;  therefore  the  coefficient  would 
be  all  — B  and  no  C  whatever. 

In  the  case  of  ship's  head  South  while  building,  the  attraction 
is  also  fore  and  aft,  and  none  athwartship ;  therefore  the  needle  is 
drawn  towards  the  bow,  giving  all  -{-B  and  no  C. 

In  the  case  of  ship's  head  East  while  building,  there  is  no  fore- 
and-aft  attraction,  but  all  athwartship,  and  as  the  North  end  of  the 
needle  is  drawn  to  the  starboard  side,  there  is  all  -\-C  and  no  B. 

In  the  case  of  ship's  head  West  while  building,  there  is  all 
athwartship  attraction,  and  none  fore-and-aft.  Here  the  needle 
IS  drawn  to  the  port  side,  therefore  there  is  all  — C  and  no  B. 

In  the  case  of  ship's  head  N.E.  while  building,  the  North  end 
of  the  compass-needle  is  drawn  equally  towards  the  stern  and  the 
starboard  side.  The  result  is  therefore  — B  and  -f  C  in  equal 
amounts. 

In  the  case  of  a  ship's  head  N.W.  while  building,  the  North  end 
of  the  needle  is  drawn  towards  the  stern  and  the  port  side  equally. 
This  would  be  — B  and  — C  in  equal  amounts. 

In  the  case  of  a  ship's  head  S.E.  while  building,  the  North  end 
of  the  needle  is  attracted  towards  the  bow  and  the  starboard  side. 
This  would  give  -)-B  and  -|-C  in  equal  amounts. 

In  the  case  of  a  ship's  head  S.W.  while  building,  the  North  end 
of  the  needle  is  drawn  to  the  bow  and  the  port  side.  This  would 
give  -|-B  and  — C  in  equal  amounts. 

The  student  Avill,  no  doubt,  understand  that  if  the  ship  was  built 
with  her  head  in  any  other  direction  than  those  given  the  value  of 
the  coefficient  would  be  different;  that  is,  if  her  head  was  N.N.E. 


FIG.  6 


(§})ips     Head 

N.E. 


FIG.  7 


FIG.8    'v  '5'l'P5     Head       „s 


Compass  Adjustment.  327 


when  building,  the  value  of  B  would  be  greater  than  C,  but  if 

built  with  her  head  E.N.E.,  the  value  of  C  would  be  greater  than  B. 

From  what  has  already  been  said,  the  following  is  deducted: 

Ship's  Head  The  North  end  of  Compass  Needle 

while  Building.  on  Bridge  will  be  Drawn. 

N.  Toward  the  stern. 

N.E.  Toward  the  starboard  quarter. 

E.  Toward  the  starboard  side. 

S.E.  Toward  the  starboard  bow. 

S.  Toward  the  bow. 

S.W.  Toward  the  port  bow. 

W.  Toward  the  port  side. 

N.W.  Toward  the  port  quarter. 

The  reader  must  understand  that  all  remarks  regarding  the  hull 
relate  exclusively  to  the  subpermanent  character  of  the  ship.  To 
further  illustrate  the  subject  the  following  table  is  given,  showing 
the  approximate  deviation : 


Ship's  Head  while 
Building. 

Approximate    Maximum 

Easterly  Deviation 

Occurs. 

Approximate  Maximum 

Westerly  Deviation 

Occurs. 

N. 

w. 

E. 

N.E. 

N.W. 

S.E. 

E. 

N. 

S. 

S.E. 

N.E. 

S.W. 

S. 

E. 

w. 

S.W. 

S.E. 

N.W. 

w. 

S. 

N. 

N.W. 

S.W. 

N.E. 

It  will  be  noticed,  in  this  table,  that  on  one-half  the  compass 
there  is  Easterly  deviation  and  on  the  other  half  Westerly  deviation, 
hence  the  name,  "semicircular  deviation." 

QUADRANTAL  DEVIATION. 

This  error  is  caused  by  the  induction  of  horizontal  iron,  such  as 
iron  beams,  either  extending  fore  and  aft  or  athwartships.  It  is 
so  named  because  it  produces  the  maximum  amount  of  deviation 
when  ship  is  heading  on  the  intercardinal  points,  namely,  N.E., 
S.E.,  S.W.,  and  N.W.,  and  is  practically  harmless  when  ship  is 
heading  on  the  cardinal  points,  namely.  North,  South,  East  and 
West. 


328  Taylor's  Modern  Navigation. 


The  effect  on  a  compass  of  horizontal  soft  iron  extending  fore- 
and-aft  or  athwartship  is  illustrated  or  named  coefficient  D.  +0 
represents  the  effect  of  continuous  athwartship  iron,  such  as  the 
ordinary  iron  beams  in  a  ship.  It  produces  -\-  or  Easterly  devia- 
tion in  both  N.E.  and  S.W.  quadrants  and  —  or  Westerly  deviation 
in  the  N.W.  and  S.E.  quadrants,  completely  disappearing  on  the 
cardinal  points,  North,  South,  East,  and  West. 

— D  represents  the  effect  of  fore-and-aft  iron,  and  is  exactly 
opposite  to  -^-D,  as  it  produces  +  or  Easterly  deviation  in  the 
N.W.  and  S.E  quadrants,  and  —  or  Westerly  deviation  in  the  X.E. 
and  S.W.  quadrants. 

— D  will  rarely  be  found  in  actual  practice,  owing  to  the  pre- 
ponderance of  athwartship  iron  over  the  smaller  amount  of  fore- 
and-aft  iron  used  in  the  construction  of  modern  vessels,  therefore 
a  -j-D  will  almost  invariably  be  found. 

It  may  not  be  amiss  to  state,  before  finishing  with  D,  that  if  a 
compass  be  placed  between  divided  iron,  such  as  in  a  hatchway  or 
a  skylight,  the  contrary  effect  to  what  has  been  said  will  be  pro- 
duced, -j-D  becoming  — D,  and  so  on ;  but  this,  also,  is  a  rare  case, 
as  no  one  would  be  so  foolish  as  to  place  a  compass  in  such  posi- 
tions, for  the  reason  that  the  iron,  being  divided,  would  act  as  two 
separate  magnets. 

CoetHcient  E  represents  the  effect  of  horizontal  iron  when  lying 
at  an  angle  of  forty-five  degrees  to  the  fore-and-aft  line,  or  in  other 
words,  it  is  caused  by  the  horizontal  iron  in  the  vicinity  of  the 
compass  not  being  symmetrically  distributed. 

+E  is  produced  by  iron  extending  from  the  starboard  quarter 
to  the  port  bow,  and  — E  when  the  direction  of  the  iron  is  from 
the  port  quarter  to  the  starboard  bow. 

If  the  compass  were  placed  between  divided  iron,  the  sign  of  the 
coefficient  would  be  changed  as  in  the  case  of  D. 

Coefficient  E  causes  quadrantal  deviation,  and  is  greatest  when 
the  ship  is  heading  North,  South,  East,  and  West,  and  is  therefore 
contrary  to  D.  -f  E  represents  -f  or  Easterly  deviation  in  the 
North  and  South  quadrants,  between  N.E.  and  N.W.  and  S.E.  and 
S.W.,  and  —  or  Westerly  deviation  in  the  East  or  West  quadrants; 
a  — E  coefficient  is  exactly  opposite,  as  —  or  Westerly  deviation,  is 
found  in  the  North  and  South  quadrants,  and  -f-  or  Easterly  in 
the  E.  or  W.  quadrants. 

Coefficient  E  is,  as  a  rule,  very  small,  and  is  closely  allied  to  a 
real  A  coefficient. 


Compass  Adjustment.  329 

COMPUTATIOX  OF  THE  COEFFICIENTS,  OR  ANALYZ- 
ING THE  NATURAL  DEVIATION  OF  A  COMPASS. 

First  swing  the  ship,  steadying  her  head  on  every  four  points, 
and  determining  the  natural  deviations  of  the  compass,  by  either 
Azimuths  or  Napier's  diagram. 

Rule  to  find  the  value  of  coefficient  A : 

Add  together  algebraically  the  deviations  found  when  ship  was 
heading  on  North,  South,  East,  and  West. 

This  is  done  by  first  naming  the  Easterly  deviations  +,  and 
Westerly  deviations  — ;  then  take  the  sum  of  the  -|-  signs  and  the 
sum  of  the  —  signs,  subtract  the  smaller  from  the  greater  and  di- 
vide by  4;  the  result  will  be  the  value  of  coefficient  A,  which  must 
be  named  according  to  the  name  of  the  greater  sum. 

Exatnple. 


[orth 

+   2°  40' 

South 

-  3°  20' 

l^est 

+  20°  50' 

+  23°  30' 

East 

-18°  10' 

-21°  30' 

-21°  30' 

4)2°  00' 

Coefficient  A  +  0°  30' 
Coefficient   B,    reverse   the   sign    of   the    deviation    found   when 
ship  was  heading  West  and  add  to  it  the  deviation  for  ship's  head 
East,  divide  the  sum  by  2.  and  the  result  will  be  the  value  of  B, 
with  the  common  sign  prefixed  to  it. 

Example. 

West  (with  sign  changed)  +19°  20' 
East  (sign  not  changed)      +18    40 

2)38~00 

Coefficient  B  +19°  00' 

Coefficient  C — This  coefficient  is  found  by  adding  together  the 
deviations  found  when  ship  was  heading  North  and  South  by  com- 
pass, changing  the  sign  of  the  deviation  for  South,  and  dividing 
the  sum  bv  2 :  the  result  will  be  the  value  of  C. 


330  Taylor's  Modern  Navigation. 


Example. 

South  (Avith  name  of  deviation  changed)  +10°  10' 
North  (with  name  not  changed)  +14    20 

2)24~~30 
Coefficient  C  +12°  15' 
Coefficient  D— Note  the  deviations  on  N.E.,  S.W.,  S.E.,  and 
N.W.  by  compass,  marking  it  +  if  Easterly  and  —  if  Westerly; 
change  the  signs  of  deviation  on  N.W.  and  S.E.  and  place  +  de- 
viations under  each  other  and  —  deviations  under  each  other;  take 
the  sum  of  the  +  signs  and  the  sum  of  the  —  signs  and  subtract 
the  sum  of  the  one  from  the  sum  of  the  other,  according  to  which 
is  the  greater  sum,  and  divide  the  difference  by  4;  the  result  will 
be  the  value  of  D,  to  which  must  be  given  the  sign  of  the  greatest 
sum 

Example. 

N.W.  (sign  changed)  +19°  30'        S.E.  (sign  changed)  -13°  20' 
N.E.  +15    20        S.W.  -  8    10 


+  34    50  -21°  30' 

-21    30 


4)13    20 
Coefficient  D  +  3°  20' 

Coefficient  E,  note  the  deviations  on  North,  South,  East,  and 
West  by  compass;  change  the  sign  of  the  last  two,  namely.  East 
and  West,  and  place  the  +  signs  under  each  other  and  the  —  signs 
under  each  other ;  take  the  sum  of  the  +  and  —  signs  separately, 
subtract  the  lesser  sum  from  the  greater  and  divide  the  difference 
by  4 ;  the  result  will  be  the  value  of  E,  to  which  must  be  given  the 
sign  of  the  greater  sum. 

Example. 

North  -  5°  10'       South  +10°  30' 

West  (sign  changed)  -12°  50'       East  (sign  changed)  +12°^0' 

-18°"  00'  +22°  50' 

-18°  00' 

4)  4°  50' 

Coefficient  E+   1°  12' 


Compass  Adjustment.  331 


COMPUTING  THE  VALUE  OF  EACH  COEFFICIENT  FOR 
EVERY    POINT    OF    THE    COMPASS. 

The  first  step  is  to  draw  a  table  in  the  same  manner  as  that  of 
the  one  attached  to  this  article,  making  a  column  for  each  coeffi- 
cient and  placing  its  value  at  the  head  of  the  column. 

A  being  a  constant  quantity  for  each  point,  its  value  and  sign 
must  be  placed  abreast  of  every  point  of  the  compass. 

B,  having  its  greatest  effect  on  East  or  West,  must  be  entered 
at  its  full  value  in  the  table,  abreast  of  those  points,  retaining  its 
sign  for  East,  but  changing  it  for  West.  The  value  of  this  co- 
efficient is  therefore  greatest  at  East  and  West,  but  is  zero  at  North 
and  South. 

Rule  to  Compute  B  for  Each  Point. 

Convert  the  value  of  B  into  degrees  and  decimals  by  simply  di- 
viding the  minutes  by  6. 

Example.— 20°  2^=  20.4.  Enter  Table  1  of  Bowditch  with 
the  number  of  points  from  North  or  South  by  compass  as  a  course, 
and  the  degrees  and  tenths  as  a  distance ;  the  departure  abreast  will 
be  the  value  of  B,  in  tenths  of  a  degree  for  the  given  number  of 
points  from  North  or  South,  and  must  be  given  the  same  sign  as 
the  coefficient  in  the  Eastern  semicircle,  but  a  contrary  sign  for  the 
Western  semicircle. 

Example. — Given  B-|-19°  50',  required  its  value  for  S.S.W. 

B  +  19°  50'-19.8    }  J.       -t;e     -A,     +u  i 

S.S.W.  =  2  points    \  ^^P-  '^■^='^  ^^"^^''  '"'^'^y- 

This  76  equals  7°. 6,  or— 7°  36'.  the  value  of  B  for  S.S.W. 

C  has  its  largest  value  at  North  and  South,  and  zero  at  East  and 
West;  therefore  place  the  full  value  of  C  with  its  proper  sign 
abreast  of  North,  and  the  same  value  abreast  of  South,  but  with  the 
sign  reversed. 

Rule  to  Compute  C  for  Each  I'oint. 

Enter  Traverse  Table  with  the  number  of  points  from  either 
North  or  South  as  a  course,  and  with  the  degrees  and  tenths  of 
degrees  of  the  value  of  C  as  a  distance,  and  take  therefrom  the 
difference  of  latitude  corresponding  thereto.  This  difference  of 
latitude  will  be  the  value  of  C,  in  tenths  of  degrees  for  the  given 
number  of  points  from  North  or  South. 


332  Taylor's  Modern  Navigation. 


Example. — Given  +C  8°  45',  required  its  value  for  N.X^. 


+  C  8°  45'  =8. 


D.  lat.  85.3  =  85  tenths 


N.XE.          =1  point 

85  tenths  equals  8.5,  or  +8"  30',  the  value  of  C  for  N.XE. 

D  is  the  greatest  on  the  quadrantal  points,  so  place  the  entire 
amount  on  N.E.,  S.E.,  S.W.,  and  N.W.,  marking  them  +  in  the 
X.E.  and  S.W.  quadrant.-;  and  —  in  the  S.E.  and  N.W.  quadrants, 
and  its  value  on  the  other  points  is  computed  by  the  following  rule : 

Bvle. 

Eeduce  coefficient  D  to  tenths  of  degrees  as  before,  and  enter  the 
Traverse  Table  with  TWICE  the  number  of  points  from  either 
North  or  South  as  a  course,  and  with  degrees  and  tenths  as  dis- 
tance, take  out  the  departure;  the  result  will  be  the  number  of 
tenths  of  degrees  for  the  given  angle. 

Example. — Given  +D  7°  6',  required  the  value  for  N.N.W. 

N.N.W.  =  2t)SnCx2  =  rpoints  |  ^^^P'  ^^-^^SO  tenths 

50  tenths  equals--5°  0',  the  value  of  D  for  N.N.W. 

E  is  greatest  on  North,  South,  East,  and  West;  therefore  place 
the  full  amount  abreast  of  those  points.  Its  value  on  the  others 
IS  calculated  by  the  following  rule : 

Bule. 

Enter  Traverse  Table  with  TWICE  the  number  of  points,  as  in 
D,  but  take  the  difference  of  latitude  as  the  value  of  E  for  the 
given  angle. 

Example. — Given  — E  1°  10',  required  the  value  for  S.S.E. 

^<?;7^°'^<?'^"^*'i   x/o      1        •   +    I  D.  lat.  8.5  =  8  tenths. 
S.S.E.  =  2  pointsX2=-4  points  ^ 

8  tenths  equal  —0°  48',  the  value  of  E  for  S.S.E. 

If  the  student  will  refer  to  the  table  of  coefficients  it  will  be 
noticed  that  the  signs  for  E  are  as  follows: 

N.W  to  N.E.,  the  same  sign  as  the  coefficient. 

N.E.  to  S.E.,  the  contrary  sign  to  the  coefficient. 

S.E.  to  S.W.,  the  same  sign  as  the  coefficient. 

S.W.  to  N.W.,  the  contrary  sign  to  the  coefficient. 

It  will  also  be  seen  that  the  value  of  B  column  increases  from 
North  or  South  to  East  or  West,  and  that  when  one  quadrant  is 
computed  it  is  not  necessary  to  compute  the  others,  as  they  have 


Compass  Adjustment. 


333 


the  same  value  throughout  each,  the  only  difterence  being  tliat  the 
Eastern  semicircle  has  a  contrary  sign  to  the  Western  semicircle. 

The  same  will  be  noticed  with  the  other  columns  in  regard  to  the 
values,  but  care  should  be  taken  in  regard  to  the  signs;  therefore, 
in  practice,  it  is  only  necessary  to  compute  the  coefficient  for  one 
cjTuidrant. 


North , 

N.XE 

N.N.E 

N.E.XN.. 

N.E 

N.E.XE. . 

E.N.E 

E.XN  

East 

E.XS 

E.S.E 

S.E.XE.. 

S.E 

S.E.XS... 
S.S.E....... 

S.XE 

South 

s.xw 

s.s.w 

s.w.xs.., 

s.w 

s.w.xw. 
w.s.w... 

w.xs 

West 

W.XN 

W.N.W.... 
N.W.XW. 

N.W 

N.W.XN.. 
N.N.W.... 
N.XW 


+0° 


+0  30 
+0  30 
+0  30 
+0 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  30 
+0  80 
+0  30 
+0  30 


B 

+17°  30' 


00  00 
+  3  24 
+  6  42 
+  9  42 
+12  18 
+  14  30 
+16  12 
+  17  12 
+  17  30 
+17  12 
+  16  12 
+  14  30 
+12  18 
+  9  42 
+  6  42 
+  3  24 

00  00 

—  3  24 

—  6  42 

—  9  42 
—12  18 
—14  30 
—16  12 
—17  12 
—17  30 
—17  12 
—16  12 
—14  30 
—12  18 

—  9  42 

—  6  42 

—  3  24 


C 

+1°30' 


+  1  30 
+  1  28 
+  1  24 
+  1  12 
+  1  0(i 
+0  48 
+0 
+0  18 

00  00 
-0  18 
— 0  36 
— 0  48 
— 1  06 
—  1  12 
— 1  24 

-  1  28 
— 1  30 
— 1  28 
— 1  24 
— 1  12 
-1  06 
-0  48 
-0  3( 
-0  18 

00  00 
+0  18 
+0  36 
+0  48 
+1  06 
+  1  12 
+1  24 
+1  28 


D 

+3°30' 


E 

-0°15 


-0  15 

-0  12 

0  09 

-0  06 

00  00 

^0  06 

4  0  09 

+0  1 

+0  15 

+0  12 

+0  09 

+0  06 

00  00 

0  06 

-0  09 

0  12 

0  15 

0  12 

0  09 

0  06 

00  00 

+0  06 

+0  09 

0  12 

0  15 

+0  12 

+0  09 

+0  06 

00  00 

-  0  06 

-0  09 

-0  12 


+  1  45 
+  6  2S 
+10  57 
+14  30 
+17  24 
+19  06 
+19  57 
+19  30 
+  18  15 
+16  18 
+  13  45 
+  11  06 
+  8  12 
+  5  42 
+  3  09 
+  0  56 

—  1  15 

—  3  16 

—  5  15 

—  7  18 

—  9  24 
—11  30 
—13  39 
—15  30 
—16  45 
—17  30 
—17  27 
—16  18 

—  14  12 
—11  18 

—  7  27 

—  2  56 


N.  48 
N.  62 
N.  75 
N.  87 
S.  81 
S.  71 
S.  62 


S. 

s. 
s. 
s. 
s. 
s. 

S.  7 
S.  17 
S.  26 
S.  35 
S.  44 
S.  53 
S.  63 
S.  73 
S.  83 
N.  84 
N.  72 
N.59 
N.  45 
N.  29 
N.  14 


45  E. 

43  E. 

27  E. 

15  E. 

24  E. 

21  E. 

27  E. 

45  E. 

45  E. 

27  E. 

45  E. 
9  E. 

48  E. 

03  E. 

21  E. 

19  E. 

15  E. 
59  W. 
15  W. 
27  W. 
36  W. 
45  W. 
51  W. 
15  W. 
15  W. 
45  W. 
57  W. 
33  W. 
12  W. 
03  W. 
57  W. 
11  W. 


PLACI]^G  THE  COMPASS. 

Select  the  position  that  the  compass  is  to  occupy,  according  to 
the  magnetic  character  of  the  ship.  This  is,  however,  rarely  pos- 
sible in  actual  practice,  as  the  bridge  is  placed,  as  a  rule,  accord- 
ing to  the  constructor's  views,  instead  of  from  the  point  of  view 


334  Taylor's  Modern  Navigation. 


of  the  navigator,  which  is  to  be  deplored,  as  the  adjuster  has  to 
contend,  through  misplacement,  with  an  error  at  times  amounting 
to  nine  or  ten  points.  Still,  the  master  should  insist  that  no  iron 
subject  to  alteration  in  its  position  shall  be  placed  within  thirty 
feet  of  the  compass,  avoiding,  as  much  as  possible,  the  bad  cases 
described  in  a  previous  part  of  this  section. 

The  position  being  selected,  next  draw  a  chalk-line  on  deck,  ex- 
actly fore  and  aft,  in  the  middle  part  of  ship ;  then  draw  another 
chalk-line  at  right  angles  to  the  first  one,  and  place  the  center  of 
the  binnacle-stand  exactly  over  the  point  of  intersection  of  the  two 
lines. 

Next  erect  a  batten  some  distance  forward  of  the  compass  and 
exactly  in  the  center  line  of  ship,  and  another  one  aft  of  compass, 
in  center  line  of  ship  also.  When  placing  the  battens,  have  them 
as  far  away  from  the  compass  as  possible,  but  with  a  clear  view 
fore  and  aft,  with  no  obstruction  between,  such  as  a  mast.  Do 
not  use  a  mark  on  a  mast  or  funnel,  as  it  may  not  be  plumb  with  the 
deck. 

Now  stand  abaft  the  binnacle  and  sight  from  the  center  of  the 
compass-bowl,  over  the  lubber-line,  to  the  forward  batten,  slewing 
the  binnacle-stand  around  until  all  three  are  in  a  direct  line,  but 
always  keeping  the  center  of  the  stand  exactly  over  the  intersec- 
tion of  the  two  chalk-lines  drawn  on  deck.  When  this  has  been 
satisfactorily  accomplished,  stand  on  fore  side  of  binnacle  and  sight 
to  the  after  batten,  then  if  the  after  batten  is  in  line  as  well  as  the 
forward  batten,  the  binnacle  is  correctly  placed;  if  not,  try  it  again, 
until  no  matter  whether  you  look  from  aft  of  compass  to  forward 
batten,  or  from  forward  of  compass  to  after  batten,  they  will  al- 
ways be  in  line  with  the  center  of  the  compass-bowl  and  the  lubber- 
line. 

Then  fasten  the  binnacle-stand  to  the  deck,  after  which  you  must 
sight  to  the  battens  as  before,  to  ascertain  if  the  stand  has  been 
moved. 

If  it  is  now  the  intention  to  adjust,  keep  the  two  chalk-lines 
drawn  on  deck,  that  is,  if  the  binnacle  is  one  that  makes  it  neces- 
sary to  use  deck  magnates,  but  if  it  is  a  modern  binnacle,  the  lines 
may  be  dispensed  with,  as  in  such  binnacles  the  interior  is  so  ar- 
ranged that  the  permanent  magnets  are  placed  on  the  inside  of  it. 

This  idea  of  placing  the  magnets  on  the  inside  of  the  binnacle 
is  an  excellent  plan,  as  the  doors  of  the  binnacles  are  closed  and 


Compass  Adjustment.  335 

locked  when  the  magnets  are  in  place,  thereby  preventing  the  med- 
dling of  people  that  may  be  too  busy  and  inquisitive. 

Two  instances  of  shifting  the  magnets  after  adjustment  came 
under  the  writers  personal  notice,  and  it  is  a  good  plan  to  men- 
tion them,  for  the  reason  that  they  place  a  navigator  on  his  guard. 

I  adjusted  the  wheel-house  compass  on  a  certain  vessel,  reducing 
the  error  to  almost  zero ;  a  few  days  afterwards  the  superint<?ndent 
of  the  company  sent  for  me,  and  said  there  must  have  been  a  ter- 
rible mistake  in  adjusting,  as  the  master  had  placed  the  vessel  on 
a  mudbank,  through  the  existence  of  a  very  large  error. 

Having  full  confidence  in  what  I  had  performed,  I  asked  him  to 
accompany  me  to  the  vessel  and  investigate.  He  did  so,  and  on 
our  arrival  on  board  we  found  that  the  master  had  shifted  the  bin- 
nacle three  inches  aft,  leaving  the  deck-magnets  as  I  had  placed 
them,  giving  as  a  reason  for  so  doing  that  the  binnacle  was  too 
close  to  the  forward  part  of  the  wheel-house  and  that  the  quarter- 
master could  not  clean  the  brasswork  unless  it  was  moved  a  little 
aft.     Of  course  the  ma5.ter's  explanation  exonerated  the  adjuster. 

Another  instance  was  the  changing  of  the  position  of  a  deck 
magnet  by  the  ship's  carpenter,  when  calking  the  deck.     In  this 
ease  the  reason  was  given,  that  the  officers  when  walking  across  the 
bridge  occasionally  stubbed  their  toes. 

CAUTION  IN  PLACING  MAGNETS. 

Permanent  magnets  must  never  be  placed  end  on  to  the  com* 
pass,  as  by  so  doing  only  one  pole  comes  into  play,  whereas  both 
poles  are  required,  as  one  end  of  a  magnet  repels  and  the  other 
attracts  the  North  end  of  a  compass-needle. 

SIZE  OF  MAGNETS. 

This  matter  depends  to  a  great  extent  on  the  position  of  the 
compass  and  the  most  convenient  places  to  which  they  may  be  se- 
cured or  fastened,  but  they  should  be  placed  as  far  away  as  con- 
venient, using  large  magnets  in  preference  to  smaller  ones,  that  is, 
if  the  deck  or  bar  magnets  are  used,  but  if  the  binnacle  is  of  mod- 
ern pattern,  having  its  interior  arranged  so  that  the  compensating- 
magnets  may  be  placed  on  the  inside,  so  that  they  may  be  raised 
or  lowered  at  pleasure,  the  matter  of  the  size  of  the  magnets  is  not 
left  to  the  discretion  of  the  adjuster. 

STRENGTH  OF  MAGNETS. 

A  magnet  should  be  of  sufficient  power  so  that  it  would  sustain  an- 
other magnet  of  equal  power  and  weight ;  this  is  always  the  case 
when  the  steel  is  properly  tempered  and  charged. 


336  Taylor's  Modern  Navigation. 

Magnets  made  of  poorly  tempered  iron  rarely  retain  for  any 
length  of  time  a  sufficient  amount  of  strength  to  lift  even  another 
magnet  of  only  one-half  its  weight. 

CARE  OF  MAGNETS. 

All  spare  magnets  should  be  tied  together  in  pairs,  with  oppos- 
ing poles  together,  and  stowed  in  some  part  of  the  ship,  away  from 
the  chronometer  and  compasses. 

If  not  tied  in  pairs,  and  allowed  to  lie  around  loose,  they  will 
lose  a  considerable  amount  of  their  power. 

PREPAEE  TO  ADJUST  THE  SHIP'S  COMPASS  AT  SEA. 

Select  a  nice,  clear,  calm  day,  and,  previously  to  adjusting,  take 
out  of  the  Sun's  True  Bearing  or  Azimuth  Tables  the  Sun's  True 
Azimuth  for  every  five  minutes  of  time,  and  convert  the  true  Azi- 
muths into  the  Magnetic  Azimuths  by  applying  the  variation  of  the 
locality,  allowing  East  to  the  left  and  West  to  the  right. 

Mark  in  a  small  book  a  sufficient  number  of  these  Magnetic  Azi- 
muths with  the  A.T.S.  to  cover  the  period  of  time  it  is  intended  to 
take  when  adjusting. 

Next  set  the  wheel-house  clock  or  a  hack  watch  to  A.T.S.  by  the 
rule  given  in  the  section  relating  to  the  finding  of  the  deviation. 

Examine  the  lockers,  if  any,  in  the  wheel-house  or  under  it  and 
see  if  they  contain  any  iron  articles  subject  to  removal. 

Examine  the  pockets  of  the  helmsman,  and  your  own  also,  re- 
moving all  iron  or  steel  articles  therefrom,  such  as  keys  or  knives. 

Have  ship  upright  and  on  even  keel,  and  see  to  it  that  all  gear, 
such  as  cargo-booms,  derricks,  and  boat's  davits,  are  in  the  posi- 
tions they  are  to  occupy  when  ship  is  at  sea. 

Clear  the  deck,  in  the  vicinity  of  the  compass,  from  all  encum- 
brances, and  remove  from  the  binnacles  all  magnets  and  soft-iron 
correctors  to  a  distance  of  at  least  sixty  feet  from  the  compass  it 
is  the  intention  to  adjust,  and  have  an  intelligent  seaman  to  keep 
meddlers  away  and  to  bring  the  magnets  to  you  as  required,  with 
instructions  not  to  bring  them  too  close  to  the  compass  when  or- 
dered to  fetch  them. 

All  now  being  ready,  proceed  to  swing  ship  and  determine  the 
natural  deviations  for  every  four  points  of  the  compass. 

First  compute  coefficient  A,  and  if  found  unusually  large,  stop 
and  investigate. 


CoM]'Ass  AojuaTniKNT.  337 


A  large  A  may  arise  from  the  retentive  magnetism  in  the  ship, 
error  in  observing,  or  it  may  be  from  a  misplaced  lubber-line. 

To  determine  if  it  is  caused  by  retentive  magnetism,  swing  ship 
again  and  find  the  deviation,  but  if  the  ship  was  turned  with,  a  port 
helm  the  first  time,  the  ship  must  be  turned  with  a  starboard  helm 
the  second  time ;  then  if  the  value  of  A  is  of  a  contrary  name,  trut 
of  equal  value  to  what  it  was  found  at  first,  it  is  proof  that  the 
cause  of  the  large  A  is  owing  to  retentive  magnetism;  therefore 
take  the  mean  of  the  two  tables  of  deviation  found  as  the  proper 
table  of  natural  deviations  for  every  four  points  of  the  compass. 

If  the  second  or  last  swing  gave  a  result  practically  the  same  as 
the  first,  then  there  must  be  an  error  in  the  position  of  the  lubber- 
line. 

If  A  is  caused  by  a  misplaced  lul)ber-line,  rule  in  a  new  one,  if 
it  is  a  dry  compass,  the  required  number  of  degrees  to  the  right 
of  its  old  position  if  the  sign  of  A  is  +,  but  if  — ,  then  move  it  to 
the  left 

Next  compute  the  value  of  B  and  C.  and  when  tliis  is  done,  sep- 
arate the  value  of  B,  due  to  the  subpermanent  magnetism  in  the 
ship,  from  that  part  of  B  due  to  the  transient  magnetism  found 
in  vertical  iron.  Here  the  importance  of  knowing  the  magnetic 
direction  of  the  ship's  head  while  building  comes  into  use,  in  con- 
■junction  with  compass-a.nalysis. 

We  have  previously  explained  that  magnetism  in  vertical  iron 
depends  for  its  strength  upon  the  magnetic  dip  of  the  locality,  and 
is  therefore  a  changeable  quantity,  whereas  the  subpermanent 
magnetism  acquired  when  building  is  practically  constant;  know- 
ing this,  the  system  of  compensation  cannot  be  the  same  for  both, 
therefore  subpermanent  magnetism  must  be  compensated  by  a  per- 
manent magnet,  but  the  transient  magnetism  must  be  compensated 
by  soft  iron  in  a  vertical  position,  called  a  "Flinders  bar"  and  must 
be  placed  on  that  side  of  the  compass  opposite  to  the  mass  of  verti- 
cal iron  which  is  disturbing  the  compass. 

Rule  to  Find  the  Amount  of  Deviation  Due  to  Vertical  Iron. 

Enter  the  Traverse  Table  in  Bowditch  with  the  magnetic  direc- 
tion of  the  ship's  head  while  being  built  as  a  course,  and  look  in 
the*  departure  column  for  the  number  corresponding  to  the  devia- 
tion on  either  North  or  South,  and  abreast  of  it,  in  the  latitude 
column,  will  be  found  the  value  of  the  subpermanent  magnetism 


338  Taylor's  Modern  Navigation. 

on  East  or  West,  which,  subtracted  algebraically  from  the  quan- 
tity actually  observed  on  one  or  other  of  those  points,  will  leave 
tlie  amount  due  to  vertical  iron.  Mark  down  the  result  ready  for 
use  when  compensating. 

Now  compute  D  and  find  its  value,  after  which  it  is  necessary 
to  select  two  spheres  of  sufficient  size  to  compensate  D,  or  the 
quadrantal  error,  as  it  is  called.  This  is  done  by  reference  to  the 
table  attached  to  this  article,  the  results  contained  therein' having 
been  observed  by  experiment,  which  any  one  can  prove,  provided 
he  is  not  afraid  of  the  expense.  Here  may  be  mentioned  a  curious 
fact,  which  is,  any  hollow  iron  cube  or  sphere  has  the  same  effect 
as  a  solid,  providing  the  thickness  of  the  shell  is  one  tenth  of  the 
thickness  of  the  whole  body,  and  also  one  sphere  used  to  correct  the 
quadrantal  error  will  compensate  one  half  as  much  as  two  of  the 
same  size  used  for  the  purpose. 

The  value  of  D,  or  the  quadrantal  error,  being  determined,  enter 
the  table  and  select  a  pair  of  globes  of  the  size  necessary  to  com- 
pensate the  quadrantal  error.  This  being  done,  we  are  ready  to 
adjust  the  compass. 

To  Adjust. 

Place  the  two  iron  spheres  on  the  brackets  at  the  sides  of  the 
binnacles,  and  as  far  away  as  possible,  but  do  not  secure  them  per- 
manently. 

Next  steady  the  ship's  head  East  or  West  magnetic  by  means 
of  the  Pelorus  (as  explained  under  heading  of  Pelorus  in  another 
part  of  this  book),  and  compensate  B  or  the  s-emicircular  devia- 
tion. 

In  this  adjustment  there  are  two  separate  compensations  to  be 
made,  thus: 

Compensate  the  deviation  on  East  or  West,  caused  by  the  sub- 
permanent  magnetism,  by  a  permanent  fore-and-aft  magnet,  placed 
at  the  side  of  the  binnacle,  with  its  center  exactly  on  the  athwart- 
slnp  line  which  passes  through  the  center  of  the  compass-card.  The 
magnet  must  also  be  parallel  to  the  fore-and-aft  line.  This  is 
assured  if  a  modern  compensating-binnacle  is  used,  but  if  deck- 
magnets  arc  used,  great  care  must  be  taken  to  place  the  magnets 
correctly  on  the  deck. 

Now,  assuming  that  deck-magnets  are  to  be  used,  and  the  ship's 
head  to  be  East  magnetic,  note  if  the  North  end  of  needle  is  drawn 
aft;  if  so,  then  place  the  North  or  red  end  of  the  magnet  aft  also; 
l)ut  if  the  North  end  of  the  needle  is  drawn  forward,  then  place 


FIG.  1 5 


Compass  Adjustment.  339 

the  red  end  of  the  magnet  forward  also;  when  this  is  done,  move  the 
magnet  slowly  towards  the  compass  until  the  amount  of  'deviation 
due  to  subpei-manent  magnetism  has  been  compensated,  then  fasten 
the  magnet  temporarily  to  the  deck. 

Flinders  Bar. 

Then  place  in  the  tube,  which  is  generally  on  the  fore  part  of  the 
binnacle,  a  sufficient  number  of  pieces  of  the  Flinders  Bar  until  the 
compass  points  East  Magnetic;  the  adjustment  is  then  finished  for 
the  time  being. 

Adjustment  on  North  or  South. 

We  will  take  North  for  the  sake  of  clearness.  The  error  to  be 
compensated  here  is  semicircular,  namely,  coefficient  C,  and  as  it 
is  due  entirely  to  the  subpermanent  magnetism,  a  permanent  mag- 
net must  be  used  to  compensate  it.  Therefore  place  ship's  head 
iS^orth  magnetic  by  Pelorus,  and  note  to  which  side  of  the  ship  the 
North  end  of  the  needle  is  attracted,  and  place  a  magnet  athwart- 
ship  on  the  deck,  with  its  middle  on  the  center  fore-and-aft  line  of 
tlie  ship,  and  with  its  red  end  to  the  same  side  of  the  ship  as  the 
North  end  of  the  compass-needle,  then  move  the  magnet  slowly 
towards  the  compass  until  the  compass  points  North  magnetic, 
and  then  fasten  the  magnet  temporarily  to  the  deck. 

Adjust  on  N.E. 

This  adjustment  can  be  made  on  any  one  of  the  quadrantal 
points,  but  we  will  select  N.E.  for  the  sake  of  example. 

Place  ship's  head  N.E.  magnetic  by  Pelorus  and  advance  both 
of  the  globes  towards  the  compass  until  the  compass  points  N.E. 
magnetic  also.  When  this  is  done,  secure  them  temporarily,  and 
then  swing  the  ship  for  remaining  errors.  It  frequently  occurs 
tiiat  one  adjustment  interferes  with  the  other;  so,  turn  the  ship's 
head  to  the  opposite  points  to  what  it  was  when  the  adjustments 
were  made,  and  touch  up  the  magnets  again  if  necessary,  until,  no 
matter  what  course  the  ship  is  steering,  no  error  can  be  detected : 
then  secure  all  magnets  permanently. 

It  is  sometimes  the  case,  however,  that  when  a  compass  is  ad- 
justed on  a  certain  point,  the  opposite  course  will  show  an  error, 
although  the  adjustment  has  been  properly  made.  The  cause  of 
this  is  an  unequal  distribution  of  iron  in  the  vicinity  of  the  com- 
pass. If  such  a  case  should  arise,  halve  the  deviation  between  two 
opposite  courses  so  as  to  make  the  remaining  error  as  small  as 
possible. 


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Compass  Adjustment.  341 

If  the  preceding  instructions  in  regard  to  adjusting  are  strictly 
carried  out,  the  navigator  will  make  a  successful  adjuster;  but  if 
there  is  an  attempt  on  his  part  to  appear  smart,  by  swinging  the 
ship  and  adjusting  in  a  very  short  space  of  time,  he  will  eventually 
find  that  the  adjustment  made,  or  remaining  errors  determined 
so  hurriedly,  will  be  far  from  l)eing  correct,  owing  to  what  is  termed 
Retentive  Magnetism. 

RETENTIVE  MAGNETISM  is  caused  by  the  inductive  force 
of  tlie  earth  acting  on  the  hull  of  the  ship,  when  she  has  been  on 
one  course  for  any  length  of  time.  Its  amount  depends  on  t"he 
length  of  time  an  iron  vessel  has  been  on  a  course  and  the  force  of 
the  waves  striking  the  ship.  It  is  a  very  variable  quantity,  and  its 
value  is  impossible  to  determine,  no  matter  how  much  scientific 
knowledge  the  adjuster  may  possess.  The  effect  on  a  compass  is 
always  a  tendency  towards  the  last  course  the  ship  was  steering. 
To  illustrate  retentive  magnetism  I  will  give  a  case: 
The  author  was  adjusting  the  compasses  of  a  very  large  iron 
steamer.  She  was  the  modem  type  of  tramp,  having  iron  decks 
and  houses,  the  bridge-deck  being  the  only  part  of  the  vessel  built 
of  wood. 

After  making  the  adjustment  on  North  correctly,  it  was  neces- 
sary to  turn  the  ship's  head  South.  On  this  being  done,  an  ap- 
parent error  of  nearly  one  point  was  detected,  which  caused  the 
ofiicers  to  east  smiling  glances  in  the  direction  of  the  adjuster. 

Noticing  this,  the  master  was  requested  to  place  one  of  his  best 
officers  at  the  Pelorus  to  take  Azimuths,  but  at  the  same  time  to 
keep  the  vessel  heading  South  by  the  compass.  This  was  done, 
and  twenty  minutes  afterwards  the  compass  was  found  to  indicate 
South  magnetic,  without  touching  the  magnet  that  had  been  placed 
to  adjust  on  North,  much  to  the  surprise  of  the  officers. 

This  was  an  extreme  case  of  retentive  magnetism,  and  is  an  ex- 
cellent illustration  of  the  bad  policy  of  performing  the  hurry-up 
jobs  one  sees  so  frequently. 

The  lesson  to  be  learned  by  the  foregoing  is,  that  a  vessel  should 
be  steadied  on  a  course  for  at  least  fifteen  minutes  before  an  obser- 
vation is  taken  to  determine  the  deviation,  and  twenty  minutes  when 
adjusting. 


342  Tayloe's  Modern  Navigation. 

FURTHER  INFORMATION  IN  REGARD  TO  THE 
FLINDERS   BAR. 

A  Flinders  Bar  is  a  bar  of  iron  from  two  and  a  half  to  four 
inches  in  diameter  and  about  two  feet  long.  This  bar  is  first  cut 
in  two  pieces,  then  one  of  the  pieces  is  again  cut  in  two,  and  yet 
again  one  of  these  pieces  is  cut  in  two ;  this  is  done  until  the  small- 
est piece  is  about  one  inch  in  length.  These  pieces  are  placed  in 
the  vertical  bra^'s  tube  attached  to  the  outside  of  a  modern  binnacle 
when  adjusting  the  semicircular  deviation  caused  by  vertical  iron. 

As  before  remarked,  the  magnetism  contained  in  vertical  iron 
depends  for  its  strength  on  the  dip  of  the  locality.  Now,  if  the  ship 
is  on  the  magnetic  equator  there  will  be  no  dip,  and  consequently 
no  magnetism  in  vertical  iron.  This  is  very  important,  as  any 
deviation  found  on  an  East  or  West  course  when  ship  is  on  the 
magnetic  equator  must  be  caused  solely  by  the  subpermanent  mag- 
netism in  the  vessel's  hull.  Knowing  this,  and  supposing  the  com- 
pass to  be  adjusted  on  East  or  West  by  a  permanent  magnet  while 
the  ship  is  on  the  magnetic  equator,  it  stands  to  reason  that  any 
deviation  subsequently  found  on  East  or  West  after  leaving  the 
magnetic  equator  must  be  due  solely  to  vertical  iron.  Therefore, 
after  changing  the  magnetic  latitude  about  twenty  or  tliirty  de- 
grees, place  ship's  head  on  East  or  West  magnetic  and  compensate 
all  the  error  found,  by  means  of  the  Flinders  bar,  on  the  principle 
that  "like  cures  like."  If  this  is  carefully  done,  the  compass  will 
have  but  a  very  small  error  in  any  latitude. 

Fig.  12  is  to  illustrate  the  effect  of  vertical  iron. 

The  compass  being  placed  between  the  two  smoke-stacks  and 
equi-distant  from  both,  the  effect  of  one  on  the  compass  will  be 
counterbalanced  by  the  other,  and  as  the  intensity  of  the  magnetism 
in  one  smoke-stack  changes,  so  it  does  in  the  other,  the  result  being 
that  neither  of  them  has  any  effect  on  the  compass. 

Again,  supposing  the  ship  to  be  in  a  South  magnetic  latitude. 
Here  the  lower  ends  of  both  smoke-stacks  would  be  blue  and  the 
upper  ends  red,  the  balance  of  power  always  being  maintained,  no 
m.atter  what  latitude  the  ship  may  be  in. 

This  is  the  principle  of  the  Flinders  Bar  adjustment,  and  with- 
out this  method  of  compensation  tlie  deviation  will  continually 
change  as  the  ship  alters  her  magnetic  latitude. 


Compass  Adjustment.  343 

RULE  TO  FIND  THE  DIRECTION  OF  THE  SHIP'S  HEAD 
WHEN  BUILT. 

This  rule  is  of  value  only  when  ship  is  on  the  magnetic  equator, 
as  at  that  time  vertical  iron  has  no  effect. 

The  value  of  the  Subpermanent  B  and  C  must  be  known. 

Rule. 

Enter  the  Traverse  Table  with  the  value  of  B  as  difference  of 
latitude  and  C  as  departure  (in  the  same  manner  as  finding  the 
course  by  inspection  in  the  Day's  Work)  and  take  out  the  course 
corresponding  thereto;  the  result  will  be  the  approximate  direc- 
tion of  the  ship's  head  when  building,  to  be  named  Xorth  if  B  is 
— ,  but  South  if  -|-,  and  towards  the  East  if  C  is  -|-  and  towards 
the  West  if  — . 

THE  HEELING  ERROR. 

The  preceding  part  anent  the  compensation  of  the  compass  er- 
rors relates  exclusively  to  conditions  when  ship  is  perfectly  upright, 
but  as  the  ship  heels  (by  the  pressure  of  the  wind  or  trimming  of 
cargo,  etc.),  another  disturbance  of  the  compass-needle  occurs,  but 
from  two  separate  causes. 

In  the  compensations  previously  described,  horizontal  force  only 
was  taken  into  consideration,  whereas  in  the  case  of  the  heeling 
error  vertical  force  must  be  considered. 

This  vertical  force  arises  from  the  change  in  the  action  of  the 
subpermanent  magnetism  acquired  when  building,  and  the  change 
in  the  character  of  horizontal  iron,  owing  to  the  horizontal  iron 
assuming  a  more  or  lesy  vertical  position  by  the  vessel  heeling. 

The  effect  on  the  compass-needle  produced  by  the  heeling  of  the 
vessel  depends  upon  the  position  of  the  subpermanent  poles  in  the 
vessel's  hull  and  the  amount  of  heel. 

The  amount  of  heeling  error  caused  by  this  subpermanent  mag- 
netism will  depend  upon  the  degree  of  heel  and  the  angle  the  com- 
pass-needle makes  with  the  ship's  line  of  force. 

The  effect  on  a  compass-needle  produced  by  the  horizontal  iron 
assuming  a  more  or  less  vertical  position,  through  the  vessel  heel- 
ing, will  depend  upon  the  magnetic  latitude,  or  dip,  in  much  the 
same  manner  as  the  effect  of  vertical  iron,  already  explained. 

The  amount  of  heeling  error  produced  by  the  horizontal  iron, 
such  as  beams,  now  assuming  a  vertical  position,  will  depend :  1.  On 


344  Taylor's  Modern  Navigation. 

the  degree  of  heel.  2.  On  the  angle  the  compass-needle  makes  with 
the  athwartship  iron;   and  3.  On  the  magnetic  latitude  of  the  ship. 

The  combined  effect  of  these  forces  acts  somewhat  different,  a> 
the  disturbing  power  of  the  vessel's  beams  varies,  whereas  the  sub- 
permanent  is  practically  constant. 

The  most  common  effect,  for  a  vessel  built  and  navigated  in 
jSJorth  latitude,  is  to  attract  the  North  end  of  the  needle  towards 
the  highest  side  of  ship ;  but  this  is  not  always  the  case,  as  some- 
times the  subpermanent  may  be  stronger  than  the  transient  power 
in  the  beams,  and  may  cause  a  deflection  of  the  needles  to  the  low 
side  of  ship. 

By  referring  to  the  colored  diagram  it  will  be  seen  that  with  the 
ship's  head  North  the  whole  of  the  upper  part  of  the  stern  is  blue, 
and  that  the  vertical  force  is  acting  downwards,  the  contrary  effect 
for  Sonth,  and  by  referring  to  some  of  the  others  it  will  be  seen 
that  blue  magnetism  is  nearer  to  the  compass,  while  in  others  the 
red  is  nearest. 

Vertical  iron  also  has  an  effect,  but  it  is  generally  very  small,  and 
in  practice  may  be  considered  a  part  of  the  others. 

Fig.  13 — ^Tliis  illustration  represents  a  vessel  in  an  upright  posi- 
tion, with  red  polarity  in  the  bottom  and  blue  towards  the  deck; 
therefore,  as  ship  is  upright,  there  cannot  be  any  heeling  error.  It 
will  be  noticed  in  this  diagram  that  the  spheres  at  the  sides  of 
ihe  compass  are  colored  blue  on  the  top  and  red  below;  this  is  the 
same  coloring  as  for  vertical  iron  in  North  magnetic  latitude.  This 
may  be  determined  by  experiment  if  the  student  is  curious,  for  by 
holding  a  sphere  with  its  top  part  near  the  North  end  of  a  compass- 
needle,  it  will  be  found  to  attract  the  North,  but  if  held  so  that  its 
lower  part  be  near  the  North  end  of  a  compass-needle,  it  will  be 
found  to  repel  a  North,  but  if  these  spheres  are  held  so  that  their 
centers  lie  in  the  same  horizontal  plane  as  the  compass-needle,  they 
have  no  effect  on  the  compass  when  ship  is  heading  on  North,  South, 
East,  or  West.  The  student  must  bear  this  in  mind  as  he  pro- 
-gresses. 

Fig.  14 — This  illustration  represents  a  vessel  heeling  to  star- 
board with  the  blue  magnetism  brought  (through  ship's  heeling) 
in  to  the  same  horizontal  plane  as  the  compass-needle.  The  error 
produced  by  the  heeling  in  this  case  should  be  compensated  by  a 
vertical  magnet  placed  directly  under  the  center  of  the  compass- 
card. 


Compass  Adjustment.  345 

Fig.  15 — This  figure  illustrates  the  effect  of  the  iron  beams  when 
ship  is  heeling  in  North  magnetic  latitude. 

P,  port  side;  S,  starboard  side;  F,  looking  forward;  C  B,  com- 
pass-bowl; M,  magnet;  V  F,  vertical  force. 

Here  the  vessel  is  heeling  to  port,  therefore  red  magnetism  is 
found  in  the  port  ends  of  the  beams,  because  it  is  nearest  to  the 
North  magnetic  pole,  and  blue  in  the  starboard  ends  because  it  is 
highest  and  therefore  farthest  from  the  North  magnetic  pole.  V  F, 
being  blue,  would  have  the  effect  of  attracting  a  North  end  of  a 
compass-needle  downwards,  and  the  blue  end  of  beams  being  on  the 
starboard  side,  their  effect  would  be  to  attract  the  North  end  of  a 
needle  to  that  side.  Now,  by  looking  carefully  at  the  coloring  of 
the  two  balls  it  will  be  noticed  that  the  top  part  of  the  compass- 
bowl  is  in  line  with  both  the  lower  or  red  part  of  the  starboard  ball, 
and  upper  or  blue  part  of  the  port  ball. 

It  will,  therefore,  be  seen  that  the  blue  part  of  the  port  ball  will 
attract,  and  the  red  part  of  the  starboard  ball  will  repel,  the  North 
end  of  a  compass-needle,  thereby  overcoming  to  a  great  extent  the 
attraction  of  the  starboard  ends  of  the  beams.  The  magnet  M  with 
the  red  end  up  will  also  tend  to  reduce  the  heeling  error.  This 
magnet  is  generally  placed  in  a  small  brass  tube  situated  in  the 
binnacle,  directly  under  the  center  of  the  card,  and  which  may  be 
raised  or  lowered  at  pleasure  by  the  adjuster. 

Fig.  16  shows  the  vessel  upright,  therefore  no  heeling  error, 
but  the  magnet  M  would  be  used  to  counteract  V  F. 

Fig.  17  shows  a  vessel  heeling  to  starboard.  The  effect  of  the 
beams  is  to  draw  the  North  end  of  needle  to  port  side.  This  is, 
however,  partially  compensated  by  the  two  balls  at  the  sides  of  the 
compass,  and  remainder  being  compensated  by  the  vertical  magnet 
M.  It  will,  therefore,  be  noticed  that  the  quadrantal  correctors  are 
not  only  used  to  compensate  the  quadrantal  deviation  but  materially 
as'sist  in  reducing  the  heeling  error. 

The  Heeling  Adjustment. 

The  old-fashioned  idea  was  to  heel  the  vessel  about  ten  degrees 
to  port  or  starboard  and  then  make  the  adjustment.  This  method 
is  obsolete,  owing  to  the  great  expense  entailed  in  listing  a  vessel, 
by  shifting  cargo,  etc.  The  modern  method  of  doing  it  is  much 
more  convenient  and  less  expensive  to  the  owners. 


346  Taylor's  Modern  Xavigatiox. 

EULE. 

Procure  a  small  dipping-needle  or  meridian-finder  with  a  spirit- 
level  attachment. 

Take  this  needle  on  shore  to  some  place  where  it  will  be  free  from 
local  attraction,  bed  it  up  level,  and  carefully  note  the  readings; 
now  take  this  needle  on  board  of  the  ship,  remove  the  compass-bowl 
to  a  good  distance,  and  place  the  dipping-needle  in  the  binnacle- 
stand,  bedding  it  up  until  its  stand  is  level  and  the  center  of  the 
dipping-needle  is  in  the  same  plane  that  the  compass-needle  oc- 
cupies when  it  is  in  its  proper  place. 

Next  place  the  proper  magnet  in  the  vertical  tube  and  raise  or 
lower  it  until  the  dipping-needle  gives  the  same  reading  as  it  had 
on  shore ;  then  remove  the  dipping-needle  and  replace  the  compass- 
bowl;  the  adjustment  is  then  finished. 

In  the  matter  of  placing  the  magnet,  it  may  not  be  too  much  to 
state  that  it  is  impossible  to  place  the  magnet  with  the  wrong  end 
up,  for  by  so  doing  it  would  be  impossible  to  make  the  dipping- 
needle  read  the  same  as  on  shore. 

Value  of  Heeling  Adjustment. 

It  will  be  noticed  by  referring  to  diagrams  15  and  17  that  the 
North  end  of  a  needle  will  be  attracted  sometimes  to  the  port  and 
sometimes  to  the  starboard  side.  Now,  suppose  that  a  vessel  is 
steering  on  a  North  course,  so  that  the  needle  would  be  at  right 
angles  to  the  beams,  and  that  she  is  rolling  in  a  seaway,  the  effect 
would  be  to  alternately  attract  the  needle  to  the  port  and  star- 
board sides ;  this  would  set  up  a  swinging  motion  of  the  card,  mak- 
ing it  very  difficult  for  the  helmsman  to  steer  a  good  course,  but  if 
the  heeling  error  is  compensated  by  the  iron  spheres  and  vertical 
magnet,  the  rolling  of  the  ship  will  be  partially  counteracted,  the 
result  being  a  comparatively  steady  card  in  all  kinds  of  weather. 

From  what  has  been  said  the  value  of  the  heeling  compensation 
will  be  understood,  but  the  navigator  should  bear  in  mind  tliat  the 
adjustment  is  good  only  for  the  latitude  wherein  it  was  made,  and 
that,  no  matter  how  accurately  the  compass  has  been  compensated, 
the  deviation  is  liable  to  alteration  at  any  time ;  therefore,  he  should 
test  the  compass  by  amplitudes  and  azimuths  whenever  possible,  re- 
membering always  that  eternal  vigilance  is  the  price  of  safety.  . 


Compass  Adjustment.     [      "'     -     ^,    347 


Fig.  18 — The  object  of  this  illustration  is  to  show^a  good  arrange- 
ment for  a  steamer's  bridge.  It  will  be  noticed  by  thKeolorifag  of 
the  vertical  iron  that  the  sliip  is  in  North  magnetic  latitude. 

The  Flinders  Bar  is  shown  on  the  fore  part  of  the  binnacle,  to 
counteract  the  effect  of  the  vertical  iron  abaft  the  compass. 

The  shafts  leading  from  the  steering-wheels  to  the  steering-engine 
are  made  of  brass  as  far  down  as  the  under  side  of  the  main  deck, 
after  which  the  shafting  is  of  steel. 

It  will  be  noticed  that  the  wheel-house  compass  is  considerably 
forward  of  the  upper  or  standard  compass;  this  is  as  it  should  be, 
for  the  reason  that  the  needle  of  one  compass  will  be  influenced  by 
the  needle  of  another  if  the  compasses  are  placed  too  close  together. 

The  ventilator  placed  on  the  fore  part  of  the  bridge,  with  its 
upper  part  colored  blue,  is  supposed  to  be  iron;  this  is  bad,  because 
the  turning  of  the  cowl  will  produce  a  variable  compass  error.  This 
iron  ventilator  should  be  removed  and  a  brass  or  copper  one  should 
replace  it. 

The  iron  travelers  and  bands  on  the  fore  boom  are  also  very  bad, 
as  they  produce  a  very  variable  compass  error ;  the  amount  of  devia- 
tion caused  thereby  will  depend  upon  the  position  of  the  boom 
and  the  direction  of  the  ship's  head.  The  traveler  will  not  always 
be  blue,  for  the  reasons  explained  in  the  description  of  horizontal 
iron,  when  held  end  on  to  the  compass.  Brass  travelers  and  bands 
should  be  substituted  for  iron  ones  in  this  case. 

With  the  two  exceptions  given,  namely,  the  iron  travelers  and 
ventilator,  the  arrangement  of  the  bridge  is  the  best  possible  for  a 
modern  steamer. 


Table  for  Working  Johnson's  Method. 


LATITUDE. 

0 

10 
12 
14 

o 

0 

1 

8 

10 

0 

12 

0 
14 

16 

18 

20 

0 

22 

24 

26 

28 

30 

32 

a 

I -00 

roi 

I -02 

I -02 

I -03 

4-85 

4-12 

I -04 

1-05 

I -06 

i-o8 

1-09 

i-ii 

I-I3 

115 

i-i8 

I 

s'67 
471 

4-OI 

570 

47Z 
4 -02 

573 
475 
4-04 

576 
478 
406 

5-79 

4-8i 
4-09 

ill 

4- 16 

5-97 
495 
4-20 

6-03 
S-oi 
4-26 

6-12 
S-o8 
4-32 

6-'2I 

5-,6 
4-38 

6-30 

5-28 
4-46 

6-^2 

5-34 
4-54 

6-5S 

5-43 
4-63 

6-69 
5-55 
473 

6 
5 
4 

16 
18 
20 

3 '49 

3 -08 
2-75 

3-50 
3-09 
276 

3-52 

1)1 

3-54 
313 
279 

3-56 

315 
2-8i 

359 
318 
2-83 

3-62 

3-20 
2-86 

3-66 
3-24 
2-89 

3-70 
3-28 
2-92 

376 
3-32 
2-96 

3-82 
3-37 
3-01 

3-88 

3-43 
3-06 

3-94 

3-49 

3-12 

4-02 

3-55 
3-17 

4-11 
3-63 
3-24 

4 
3 
3 

22 
24 
26 

2-47 
2-25 
2-05 

2-47 
2-26 

2-05 

2-48 
2-27 

2-07 

2-SO 
2-28 

2-o8 

2-52 
2-30 
^•10 

2-54 
2-32 

2- 1 1 

2-57 
2-34 
2-13 

2-6o 

2-37 
2-15 

2-63 
2-39 
2-18 

2-66 
2-43 

2*21 

2-70 
2-46 
2-24 

2-75 
2-50 
2-28 

2-80 

2-55 
2-32 

2-86 
2-59 
2-37 

2-92 
2-65 
2-42 

2 
2 
2 

28 
30 
32 

1-88 

173 
I -60 

1-83 

173 
I -60 

1-90 

1-91 
176 
163 

1-92 

177 
1-64 

1-94 
1-78 
1-65 

1-96 
1-80 
1-66 

1-68 

2-00 
1-84 
1-70 

2-03 
1-87 
1-73 

2-06 
1-89 
175 

2-09 
1-92 
1-78 

2-13 

1-96 

I-8I 

2-17 

2-00 
1-85 

2*22 
2-04 
.-89 

2 

■ 

34 
36 
38 

1-48 
.•38 

1-28 

1-48 
1-38 

1-28 

1-49 

1-50 
1-40 
1-29 

1-51 
1-41 

1-30 

1-53 
1-42 
1-31 

'•54 
1-44 
1-32 

1-56 
'•45 
1-34 

1-57 
I  "47 
1-35 

I -60 

1-49 
1-37 

I-$2 

1-5* 
1-39 

1-65 

1-53 
141 

1-68 

155 
1-44 

171 
1-59 

h-48 

1-51 

40 

42 
44 

1-19 
rii 

1-04 

1-19 

I'll 

I -04 

1-20 
1"I2 

I -04 

1-21 
113 

1-05 

1-22 
114 
1-06 

1-23 
I-I4 

1-07 

1-24 
1-15 

1-08 

1-25 
1-17 
1-09 

1-27 

1-18 
i-io 

1-28 
I-20 
I-I2 

1-30 
1-22 
113 

1-32 
1-24 
VIS 

1-35 
1-26 
117 

1-28 

I-20 

1-41 

.1-31 

1-22 

46 
48 
50 

0-97 
0*90 
0-84 

o-^7 
0-90 
0-84 

0-98 
085 

098 
0-91 
085 

0-99 
0-92 
0-86 

i-oc 
0-93 
0-87 

I  01 

0-94 
087 

1-02 
0-95 
0-88 

1-03 
0-96 
0-89 

1-04 
0-97 
0-91 

1-06 
0-99 
0-92 

1-07 
i-oo 
0-93 

1-09 
I -02 
0-95 

I-Il 

1-04 

0--97 

I-I4 

I -06 
0-99 

52 
54 
56 

078 
073 
o'bj 

0-78 
073 
o'bj 

079 
073 

0-68 

079 
074 
068 

0-80 
C-74 
0-69 

0-80 

075 
0-69 

0-81 
0-75 
6-70 

0-82 
0-76 
0-71 

0-83 
0-77 
0-71 

0-84 
C-78 
0-72 

o-8s 
0-79 
073 

0-87 
0-81 
0-75 

0-88 
0-82 

0-77 

0-90 
0-84 
0-78 

0-92 
0-86 
0-79 

0 
0 
0 

58 
60 
62 

0-63 
0-58 
0-53 

o'63 
0-58 
o'53 

0^63 
0-59 
0-54 

063 
059 
.0-54 

0*64 
0-59 
0-54 

0-64 
o-6o 
0-55 

0-65 
0-60 
0-55 

0-66 
0-61 
0-56 

0-66 
0-62 
0-56 

0-67 
0-62 

0-57 

0-68 
0-63 
0-58 

0-69 
0-65 
0-59- 

0-71 
0-66 
0-60 

0-72 
0-67 
0-61 

0-74 
0-68 
0-63 

0 
c 
0 

64 
66 
68 

0-49 
0-45 
0-40 

049 
0-45 
0-40 

0-50 
0-45 
0-40 

0-50 

0-4S 
0-41 

0-50 
0-46 
0-41 

0-51 
0-46 
0-41 

0-51 

0-46 
0-42 

0-52 
0-47 
0-42 

0-52 
0-47 
0-43 

0-53 
048 
0-43 

0-S4 
0-49 
0-44 

o-ss 
0-50 
0-45 

0-56 
0-50 
0-45 

0-56 
0-51 
0-47 

0-57 
0-52 
0-47 

0 
0 
0 

70 
72 
74 

0-36 
0-33 

0'29 

0-36 

0-33 
0*29 

0*36 

0-33 
0-29 

0-37 

0-33 
029 

0-37 
0-34 
0-30 

0-37 
0-34 
0*30 

0-37 
0-34 
0-30 

0-38 
0-34 
0-31 

0-38 
0-3S 
0-31 

0-39 
0-35 
0-31 

0-39 
0-36 
0-32 

0-40 
0-36 
0-32 

0-41 
0-37 
0-33 

0-42 
0-37 
0-33 

0-43 
038 
0-34 

0 
0 
0 

76 
78 
80 

0-25 

0-2I 

o-i8 

0-25 

0-21 

o-i8 

0-25 

0-2I 

o-i8 

0-2  5 
0-2I 

o-i8 

0-25 
0-21 
018 

0-26 
0-22 
o-i8 

0-27 

0-22 

o-i8 

0-27 
0-22 
0-18 

0-27 
0-22 
019 

0-27 

0-23 

0-19 

0-27 
0-23 
019 

0-28 
0-23 
0-20 

0-28 
0-23 

0-20 

0-29 
0-24 
0-20 

0-29 
0-25 
0-21 

0 
0 
0 

82 
84 
86 

0-14 
o-io 
0*07 

0-I4 
o-io 
o"07 

0-14 
o-io 
0-07 

0-14 

o-io 
0-07 

0-I4 

O-IO 

0-07 

0-14 

O-IO 

0-07 

0-I4 
o-ii 
0-07 

o-is 
o-ii 
0-07 

o-is 
o-ii 

0-07 

0-15 

O-II 

0-08 

0-15 

O-II 

0-08 

0-15 
0*11 
o-o8 

O-IS 
o-ii 

0-08 

0-16 

0-12 
0-08 

0-17 
0-12 
0-08 

0 
0 
0 

88 
89 

0*03 
o-oi 

0-03 
o-oi 

0-03 

O-OI 

0-04 

O-OI 

0-04 
001 

0-04 

O-OI 

004 

O-OI 

0-04 

0-01 

0-04 

O'OI 

0-04 

O-OI 

0-04 
001 

0-04 

O-OI 

0-04 

O-OI 

0-04 
O-OI 

0-04 
001 

0 
0 

90 

O'OO 

0*00 

O'OO 

0-00 

000 

o-co 

o-oo 

o-oo 

0-00 

000 

0-00 

0-00 

0-00 

O'OO 

OOD 

0 

o-oo 

0-07 

0'I4 

0  18 

0-2I 

0-25 

0-29 

0-33 

0-36 

0-40 

0-45 

0*49 

0-53 

0-58 

0-63 

0 

This  table  is  taken  from  Johnson's  Latitude  and  Longitude  in  Cloudy  Weather,  published  by  J.  D.  P^ 
145  Mlnorles,  London,  E.,  and  is  printed  here  by  the  express  permission  of  the  author,  Mr.  A.  C.  Johnso 


Table  for  WouKiNf;  Johnson's  Method 


LATITUDE. 

■i 
« 

"^ 

12 
14 

0 

0 

0 
34 

36 

38 

40 

42 

0 

44 

46 

48 

50 

52 

54 

56 

58 

60 

a 

ye? 

471 
4-01 

121 

6-84 
567 
4-84 

I -24 

7-01 
S-8i 
4-95 

1-^7 

1-31 

1-35 

6-33 
5-40 

1-39 

7-88 
6-S4 
5-S« 

1-44 

8 -'16 

677 
577 

1-49 

7-03 
5-99 

1-56 

8-82 
7-32 
6-24 

1 62 

1-70 

179 

i-i>9 

2  00 

7-20 

5-97 

5  09 

7-40 

6-14 
5-23 

9-21 

7 '64 
6-5. 

9-65 

8-00 

6-82 

/ 
10-14 
8-41 
7-17 

/ 
10-70 
8-88 
7-57 

/ 
11-33 
9-41 
8   02 

16 
18 
20 

3'49 
3-o8 
275 

4-2  1 

371 
3-31 

4-31 
3-8o 

3-39 

4-43 
3-90 

3 '49 

4"55 

4-02 

3*59 

4-69 
414 

370 

4-85 
4-28 
382 

5-02 
4-43 
3  95 

5-21 
4-6o 
411 

5-42 
479 
4-27 

5-66 
5-00 
4-46 

5'93 
4-67 

6-24 

5' 50 
4-91 

6-58 
5-8i 

5-19 

6-97 
6-15 
5-49 

22 
24 
26 

2'-47 
2-25 

2 '05 

2-98 
171 
2:47 

3-o6 
277 
^'53 

2-6o 

3-23 

I'll 

333 

302 
2-76 

3  "44 

3-12 

2-85. 

3-56 
3-23 
295 

3 -70 
3-36 
3-06 

3-85 

3-49 
3-19 

4-02 
3-6S- 
3'33 

4-21 

3-82 
3-49 

4-43 
4-02 
3-66 

4-67 
4-24 
3-87 

495 
4-49 
4-10 

28 
30 
32 

1-88 

173 
I -60 

2-27 
209 
1-93 

2-32 
214 
1-98 

2-39 
2 -20 

2-03 

2-09 

2-53 
2-33 
2-15 

261 

2-41 

2-22 

2-71 
2-49 
2-30 

2-8i 
260 

2-39 

2-92 
2-69 

2-49 

3 -OS 
2-8i 
2-6o 

3-20 
295 
2-72 

3-36 
3-10 
2-86 

3'55 
3-27 
3-02 

376 
346 

3-20 

34 
36 
38 

1-48 
138 

1-28 

179 

1-66 

'•54 

1-83 

170 
1*58 

1-88 
174 
I  62 

I'll 

167 

1-99 

1-85 
1-72 

2-06 
1-91 

178 

2-13 

,•98 
1-84 

2:22 

2-06 
I-9I 

2-31 
2-14 
1-99 

2-41 

2-24 

2 -08 

2-52 
2'34 
2-.8 

2-46 
2-29 

2-80 
2-6o 

2-41 

2-96 

275 
2-56 

40 
42 
44 

i-ig 
III 

I -04 

1-44 
1-34 

1-25 

I '47 
1-37 
1-28 

1-51 
1. 41 
1-31 

1-55 
1-45 
>-35 

I  60 
I  49 
139 

>-66 
'•54 
1-44 

1-72 
I -60 
1-49 

178 

1-66 
'■55 

1-85 

1-94 

1-80 

1-68 

2-03 

2-13 

2-25 
2-09 
'•95 

2-38 
2-22 
2-07 

46 
48 
50 

0-97 
0-90 
0-84 

ri6 
1-09 
roi 

1-19 
III 
1-04 

1-23 

1-14 
I -06 

1-26 
I-I7 
1-09 

1-30 

I -21 

i"i3 

1-34 

'•39 
1-30 
1-21 

1-44 
'■35 

1-25 

1-50 
1-40 
1-31 

1-56 
1-46 
.•36 

1-64 

■•53 
I  43 

1-50 

1-82 

1-70 
1-58 

III 

1-68 

52 
54 
56 

078 
073 
0-67 

0-94 
0-88 
o-8i 

0-96 

0-99 
0-92 
0-85 

I -01 

0-95 
0-88 

I -OS 
0-98 
0-91 

1-09 

l-oi 

0-94 

I  '12 

I -04 
0-97 

I-I7 
1-09 
i-oi 

1-22 
I-I3 

ro5 

1-27 

ri8 

IIO 

'•33 
123 
I-I5 

1-40 
1-30 

I-2I 

'•47 
1-37 

1-27 

1-56 
'•45 
'•35 

58 
60 
62 

0-63 
0-58 
0-53 

075 
070 
0-64 

077 

071 

0-66 

079 
073 
0-67 

081 

075 
0-69 

0-84 
0-78 
0-72 

0-87 

o-8o 
074 

0-90 

0-83 
0-70 

0-93 
0-86 
079 

0-97 
0-90 
0-83 

I-OI 

0-94 

0-86 

I -06 

0-98 
0-90 

1*12 

1-03 
0-95 

i-i8 
1-09 
I  00 

1-25 
1-15 
1-06 

64 
66 
68 

0-49 

045 
0-40 

0-59 
0-54 
0-49 

o-6o 

o'55 
0-50 

0'62 

0-56 

0-51 

0-64 
0-58 
0-53 

0-66 
o-6o 
0-54 

0-68 
0-62 
0-56 

0-70 
0-64 
0-58 

073 
0-66 
0-60 

0-76 
0-69 
0-63 

0-79 
0-72 
0-65 

0-83 
076 
0-69 

0-87 
0-79 
0-72 

0-92 
0-84 
0-76 

0-97 
0-89 
081 

70 
72 
74 

0-36 

0-33 
0-29 

0-44 

o"39 
0-34 

0-45 
0-40 
0-36 

0-46 
0-41 

0*36 

0*47 
0-42 
0-37 

0-49 
0-44 
0-38 

0-51 
0-45 
0-40 

0-52 
0-47 
0-41 

0-S4 
c-49 
0-43 

0-57 
0-51 
0-44 

0-59 
0-53 
0-46 

0-62 

o*55 
0-49 

0-65 
0-58 
0-52 

0-68 
0-61 
0-54 

0-73 
0-65 

0-5: 

76 
78 
80 

0-25 

0-21 

o-i"8 

0*30 
0-25 

C-2I 

0-31 

0'26 
0"22 

0-31 

0-27 
0-22 

0-32 
0-28 
0-23 

0-33 
0-29 

0-24 

0-34 
0-29 
0-24 

0-36 
0-30 

0-25 

0-37 
0-32 
0-26 

0-39 
0-33 
0-27 

0*40 
0-34 
0-29 

0-42 
0-36 
0-30 

0-45 
0-38 
0-31 

0-47 
0-40 
0-33 

0-50 
0-42 
0-35 

82 
84 
86 

0-14 
0  10 
0-07 

0-17 
0*13 
o'o8 

0-I7 
0-I3 

o-o8 

o-i8 
0-I3 
0-09 

o-i8 
0-14 
0*09 

c-19 
0-14 
0-09 

0-19 

0-14 
o-io 

0-20 

o'i5 
o-jo 

0-2I 

o-i6 
o-io 

0-22 
o-j6 
o-ii 

0-23 
C-17 
o-ii 

0-24 
0-18 
0-12 

0-25 
0-19 
012 

0*26 
0-20 
0-13 

0-28 

0'2I 
014 

88 
89 

0-03 

O'OI 

0*04 

O'OI 

0-04 
o-oi 

0-04 

O-OI 

0^04 

O'OI 

0-05 

O'OI 

0-05 

O-OI 

0-05 

0-0  I 

0-C5 
0-02 

0-05 
0-02 

0-06 

0-C2 

c-06 
0-02 

006 
002 

0-07 
0-02 

0-07 
0-02 

90 

0  00 

O'OO 

o-oo 

o-oo 

O'OO 

o-oo 

0-oc 

0-97 

o-oo 

1-04 

o-oo 

o-oo 

O-OO 

0-00 

0-00 

o-oo 

0-00 

o-oo 

067 

073 

0-78 

0-84 

0-90 

ril 

I-I9 

1-28 

— 

1-48 

1 60 

173 

This  table  is  taken  from  Johnsons  Latitude  and  Longitude  tn  Cloudy  Weather,  published  by  J.  D.  Potter, 
145  Minories,  London,  E.,  and  is  printed  here  by  the  express  permission  of  the  author,  Mr.  A.  C.  Johnson. 


Table  to  Correct  the  Observed  Altitude  of  the  Sun' 
(For  Practice  at  Sea.) 


Lower  Limb. 


1  Obs. 
Alt. 

UEIOUT    OF    THE    EYE    ABOVE    THE 

BEA    IH    FEET. 

6 

H 

10 

12  1    14 

16 

18  ;  20 

22  (  24 

26  1  28 

30  1  32 

34 

36 

5     0 

3.8 

3.5 

/ 
3.1 

'     i    ' 
2.8    2.5 

2.3 

2.1    1.8 

1.6 

1.4 

1.2 

1.0 

0.8'  0.6 

0.5 

0.3 

6  20 

4.3 

4.0 

3.6 

3.3!  3.1 

2.8 

2.6    2.3 

2.1 

1.9 

1.7 

1.6 

1.3    1.1 

l.O 

0.8 

5  40 

4.8 

4.5 

4.1 

3.8    3.5 

3.3 

3.1    2.8 

2.6 

2.4 

2.2 

2.0 

1.8  l.b 

1.5 

1.3 

6     0 

5.3 

4.9 

4.6 

4.3    4.0 

3.7 

3.5    3.3 

3.0 

2.8 

2.6 

2.4 

2.2  2.1 

1.9 

1.7 

6  20 

5.7 

5.4 

5.0 

4.7    4.4 

4.  1 

3.9'  3.7 

3.3 

3.2 

3.0 

2.8 

2.6 

2.5 

2.3 

2.0 

C  40 

6.0 

5.7 

5.3 

5.0    4.7 

4.6 

4.3 

4.0 

3.8 

3.6 

3.4 

3.2 

3.0 

2.8 

2.7 

2.3 

7     0 

6.4 

6.0 

5.7 

6.4!  5.1 

4.8 

4.6 

4.4 

4.1 

3.9 

3.7 

3.5 

3.3 

3.2 

3.0 

2.7 

•  7  20 

6.7 

6.31  6.0 

5.7 

5.4 

6.1 

4.9 

4.7 

4.4 

4.2 

4.0 

3.8 

3.6 

3.5 

3.3 

3.1 

7  40 

6.9 

6.6,  6.2 

5.9 

5.7 

5.4 

6.2 

4.9 

4.7 

4.5 

4.31  4.1 

3.9 

3.8 

3.6 

3.4 

8     0 

7.2 

6.8j  6.5 

6.2 

6.9 

6.7 

6.4 

5.3 

5.0 

4.8 

4.6    4.4 

4.2 

4.0 

3.9 

3.7 

8  20 

7.5 

7.11  6.7 

6.5 

6.2 

5.9 

6.7 

5.5 

6.2 

5  0 

4.81  4.6 

4.4 

4.3 

4.1 

3.9 

8  40 

7.7 

7-3!  7.0 

6.7 

6.4 

6.1 

5.9 

5.7 

5.5 

5.2 

5.01  *-8 

4.7 

4.5 

4.3 

4.1 

9     0 

7.9 

7.5 

7.2 

6.9 

6.6 

6.4 

6.1 

6.9 

5.7 

5.5 

6.31  5.1 

4.9 

4.7 

4.5 

4.4 

9  20 

8.1 

7.7 

7-4 

7.1 

6.8 

6.6 

6.3 

6.1 

5.9 

5.7 

5.5    5.3 

5.1 

4.9 

4.7 

4.6 

9  401   8.3 

7.9 

7.6 

7.3:  7.0 

6.7 

6.6 

6.3 

6.1 

5.8 

5.6    5.4 

5.3 

5.1 

4.9 

4.7 

10     0    8.5 

8.1 

7.8 

7.5|  7.2 

6.9 

C.7 

6.5 

6.2 

6.0 

6.8    5.6 

5.4 

5.3 

6.1 

4.9 

10  30|   8.7 

11  0,   8.9 

8.3 

8.0 

7.71  7.4 

7.2 

6.9 

6.7 

6.5 

6.3 

6.1    6.9 

5.7 

5.5 

5.4 

6.2 

8.6 

8.2 

7.9 

7.6 

7.4 

7.2 

6.9 

6.7 

6.5 

6.3i  G.l 

5.9 

5.7 

5.6 

5.4 

11  30,   9.1 

8.8 

8.4 

8.1 

7.8 

7.6 

7.4 

7.1 

6.9 

6-7 

6.5 

6.3 

6.1 

5.9 

5.8 

6.6 

12     0    9.3 

9.0 

8.7 

o.a 

8.0 

7.8 

7.6 

7.3 

7.1 

6.9 

6.7 

6.5 

6.3 

6.2 

6.0 

5.8 

13     0    9.6 

9.3 

9.0 

8.7 

8.4 

8.1 

7.9 

7.7 

7.4 

7.2 

7.0 

6.8 

6.6 

6.5 

6.3 

6.1 

14     O!   9.9 

9:6 

9.2 

8.9 

8.7 

8.4 

8.2 

7.9 

7.7 

7.5 

7.31  7.1 

6.0 

6.3 

6.6 

6.4 

15     0  10.2 

9.8 

9.5 

9.2 

&9 

C.7 

8.4 

8.2 

8.0 

7-8 

7.6 

7.4 

7.2 

7.0 

6.9 

6.7 

IG     0  10.4 

10.1 

9.7 

9.4 

9.1 

8.9 

8.7 

8.4 

8.2 

8.0 

7.8 

7.6 

7.4 

7.2 

7.1 

6.9 

17    oio.cib.s 

9.9 

9.6 

9.3 

9.1 

8.9 

8.6 

8.3 

8.2 

8.0 

7.8 

7.6 

7.4 

7.3 

7.1 

18     O!l0.810.4 

10.1 

9.8 

9.5 

9.3 

9.0 

8.8 

8.6 

8.4 

8.2 

8.0 

7.8 

7.6 

7.6 

7.3 

19     0,11.010.6,10.3 

10.0 

9.7 

9.4 

9.2 

9.0 

8.8 

8.5 

8.3 

8.1 

8.0 

7.8 

7.6 

7.4 

20     Oill.  110.710.4  10.1 

9.8 

9.6 

9.3 

9.1 

8.9 

8.7 

8.5 

8.2 

8.1 

7.9 

7.7 

7.6 

21     0'U.'2!l0.9:i0.510.2l0.O 

9.7 

9.5 

9.2 

9.0 

8.8 

8.6 

8.4 

8.2 

8.1 

7.9 

7.7 

22     0;11.4;il.0|10.7|10.4,10.1 

9.8 

9.6 

9.4 

9.1 

8.9 

8.7 

8.5 

8.3 

8.2 

8.0 

7.8 

23     0 

11.511.110.810.510.2 

9.9 

9.7 

9.6 

9.2 

9.0 

8.8 

8.6 

8.4 

8.3 

8.1 

7.9 

24     0 

11.611.210.910.6:10.3 

10.0 

9.8 

9.6 

9.3 

9.1 

8.9 

8.7 

8.5 

8.4 

8.2 

8.0 

25     0 

11.711.3:11.010.  7|10.4 

10.1 

9.9 

9.7 

9.4 

9.2 

9.0 

8.8 

8.6 

8.5 

8.3 

8.1 

26     0 

11. 7[11. 411. 010.710.5 

10.2,10.0 

9.7 

9.5 

9.3 

9.1 

8.9 

8.7 

8.6 

8.4 

8.2 

27     0 

11.8  1'.. Sin.  l!l0.8il0.5 

10.3110.1 

9.8 

9.6 

9.4 

9.2 

9.0 

8.8 

8.6 

8.6 

8.3 

28     0 

11. 911. 6111. 2110.910.6 

10.4!l0.2 

9.9 

9.7 

9.5 

9.3 

9.1 

8.9 

8.7 

8.6 

8.4 

30     0 

12. 0  11.7111.311.0  10. 8|10. 510. 3il0. 0 

9.8 

9.6 

9.4 

9.2 

9.0 

8.9 

8.7 

8.5 

32     0 

12.  2  11.8111.5:11.2  10.  9110.6:10.4110. 2 

9.9 

9.7 

9.5 

9.3 

9.1 

9.0 

8.8 

8.6 

34     0 

12.3111.911.6111.311.0 

10.710.510.3 
IO.8IO.61IO.4 

10.1 

9.9 

9.6 

9.4 

9.2 

9.1 

8.9 

8.7 

36     0 

12.4;i2.0lll.7 

11.4  11.1 

10.2 

9.9 

9.7 

9.6 

9.3 

9.2 

9.0 

8.8 

38     0 

I2.5I12.I 

11.8 

11.511.2 

10.910.710.5 

10.2 

10.0 

9.8 

9.6 

9.4 

9.3 

9.1 

8.9 

40     0 

12.5  12.2 

11.8 

11.6111.3 

11.010.8|l0.5 

10:8 

10.1 

9.9 

9.7 

9.5 

9.4 

9.2 

9.0 

42     0 

12.612.2 

11.9 

11.611.3 

11.1 

10.810.6 

10.4 

10.2 

10.0 

9.8 

9.6 

9.4 

9.3 

9.1 

44     0 

12.7,12.3 

12.0 

11.7 

11.4 

U.l 

10.910.7 

10.5 

10.2 

10.1 

9»8 

9.7 

9.5 

9.3 

9.1 

46    0 

12.7112.4 

12.0 

11.7 

11.6 

11.2 

11.0 

10.7 

10.5 

10.3 

10.2 

9.9 

9.7 

9.6 

9.4 

9.2 

48     0 

12.8:12.4 

12.1 

11.8 

11.5 

11.3 

11.0 

10.8 

10.6 

10.4 

10.2 

10. 0 

9.9 

9.6 

9.5 

9.3 

50     0 

12  8I2.5I12.2 

11.9 

11.6 

11.3 

11.1 

10.9 

10.6 

10.4 

10.3 

10.0 

9.8 

9.7 

9.5 

9.3 

52     0 

12.9  12.5 

12.2 

11.9 

11.6 

11.4 

11.1 

10.9 

10.7 

10.6 

10.3 

10.1 

9.9 

9.7 

9.6 

9.4 

64     0 

13.0  12.6 

12.3 

12.0 

11.7 

11.4 

11.2:11.0 

10-7 

10.5 

10.3 

10.1 

10.0 

9.8 

9.6 

9.4 

56     0 

13.0,12.6 

12.3 

12.0 

11.7 

11.5 

11.2,11.0 

10.8 

10.6 

10.4 

10.2  10.0 

9.8 

9.7 

9.6 

58     0 

I3.0I12.7 

12.3 

12.0 

11.7 

11.5 

II.3I1I.O 

lO.R 

10.6 

10.4 

IO.21IO.O 

9.9 

9.7 

9.5 

60     0 

13.lll2.7!l2.4 

12.1 

11.8 

11.611.311.1 

10.9  10.6 

10.4 

10. 2' 10.1 

9.9 

9.7 

9.5 

62     OJl.S.  1 

12.8,12.4 

12.1:11. 8:11. will. 411. 1110.910.7 

10.610.3110.1 

9.9 

9.8 

9.6 

64     ©13.2 

12.  8112.  5 

12.211.911.611.411.2,10.910.7 

16.6 

10.3  10.1 

10.0 

9.8 

9.6 

C6    o|ia.2 

12.8  12.5 

12.2'll. 911. 7!ll. 411.2111. 010.8 

10.6 

10.4fl0.2 

10.0 

9.8 

9.7 

70     0 

13.3 

12.912.6 

12.312.0  11. H 

11. 5;ll. 311. 0,10.8 

10.6 

IO.4IIO.2 

10.1 

9.9 

9.7 

80     0 

13.4 

13.1  12.7 

12.4|12.  1I1I.9 

11.7111.411.2111.0 

10.8 

10.61 10. 4 

10.2 

10.1 

9.9 

90     0 

13.G  13.2!l2.9 

12.612.3112.0 

11.811.6,11.3111.1 

10.9M0.7110.6 

10.4 

10.2|10.0| 

Month j  Jan.  1  Feb.  1  .Mar.  |April,|  JVlayJ  June,  July,  1  j 

Correction! +0'.3|-|-0'.2J+0'.l|  O'.O  |-0'.2|-0'.2  -0.31- 

\\xg.    Sept.  1  Oit.    Nov.    Dec. 

-0'.2  -O'll+O'.l  +0.2  ^O-J 

NAUTICAL  ALMANAC 
ELEMENTS 

FOR    THE    WORKING    OF    PROBLEMS 
CONTAINED  IN  THIS  BOOK. 


JANUARY,  1894. 


AT   GREENWICH   APPARENT  NOON. 


THE  SUN'S 

5 

Sidereal 

Equation 

s. 

Semi- 

to  be 

5 

diameter 

Added  to 

o 

Apparent 

Diff.  for 

Apparent 

Diff.  for 

Semi- 

Passing 

Apparent 

Diff.  for 

1 

Right  Ascension. 

1  Hour. 

Declination. 

1  Hour. 

diameter. 

Meridian. 

Time. 

IHour. 

h     m       s 

s 

g 

m      s 

s 

1 

18  48  22.70 

11.040 

S.22  59  21.9 

12.76 

16  18.36 

71.05 

3  52.72 

1.180 

6 

19  10  22.88 

10.957 

22  28  10.2 

18.41 

16  18.28 

70.77 

6    9.73 

1.097 

7 

19  14  45.60 

10.936 

22  20  35.2 

19.51 

16  18.25 

70.70 

6  35.82 

1.076 

13 

19  40  50.20 

10.788 

21  25  59.3 

25.91 

16  18.00 

70.24 

9    0.68 

0.928 

14 

19  45    8.77 

10.759 

21  15  24.9 

26.93 

16  17.94 

70.15 

9  22.63 

0.900 

15 

19  49  26.65 

10.731 

21    4  26.2 

27.94 

16  17.88 

70.05 

9  43.89 

0.871 

16 

19  53  43.82 

10.701 

20  53    3.4 

28.95 

16  17.81 

69.96 

10    4.45 

0.842 

17 

19  58    0.28 

10.671 

20  41  16.8 

29.94 

16  17.74 

69.87 

10  24.29 

0.812 

22 

20  19  11.32 

10.512 

19  36  38.7 

34.65 

16  17.29 

69.35 

11  52.30 

0.654 

26 

20  35  54.22 

10.381 

18  38  22.8 

38.14 

16  16.82 

68.92 

12  48.83 

0.523 

27 

20  40    2.98 

10.348 

18  22  57.1 

38.98 

16  16.69 

68.80 

13    0.98 

0.490 

28 

20  44  10.92 

10.315 

18    7  11.5 

39.81 

16  16.55 

68.69 

1312.35 

0.457 

FEBBUAEY. 


2 

21    4  38.64 

10.147 

16  43  37.5 

43.68 

16  15.81 

68.12 

13  57.15 

0.290 

4 

21  12  44.05 

10.079 

16    8    6.0 

45.12 

16  15.49 

67.89 

14    9.42 

0.222 

5 

21  16  45.54 

10.045 

15  49  55.0 

45,80 

16  15.32 

67.78 

14  14.34 

0.188 

6 

21  20  46.22 

10.011 

15  31  27.6 

46.47 

16  15.15 

67.66 

14  18.46 

0.154 

11 

21  40  37.47 

9.844 

13  55  22.2 

49.54 

16  14.28 

67.10 

14  26.90 

0.012 

12 

21  44  33.34 

9.811 

13  35  26.5 

50.10 

16  14.09 

66.99 

14  26.21 

0.045 

21 

22  19  22.71 

9.544 

10  26  59.6 

54.37 

16  12.26 

66.09 

13  46.70 

0.312 

22 

22  23  11.44 

9.518 

10    5  10.0 

54.76 

16  12.03 

66.00 

13  38.90 

0.338 

28 

22  45  51.57 

9.378 

7  51  11.9 

56.78 

16  10.60 

65.50 

12  39.86 

0.477 

JANUARY,  1894. 


AT  GREENWICH   MEAN   NOON. 


THE 

SUN'S 

J3 
1 

Equation  of 
Time, 

Sidereal 

Time, 

^ 

to  be 

or 

5 

Subtracted 

Right  Ascension 

o 

Apparent 

Diff.  for 

Apparent 

Diff.  for 

from 

Diff.  for 

of 

1 

Right  Ascension. 

1  Hour. 

Declination. 

1  Hour. 

Mean  Time. 

1  Hour. 

Mean  Sun. 

h     m      s         '       s 

m       s 

s 

h    m       s 

1 

18  48  21.98   11.036 

S.  22^59' 22.7 

12'.'74 

3  52.64 

1.180 

18  44  29.34 

6 

19  10  21.75   10.954 

22  28  12.2 

18.40 

6    9.61 

1.097 

19    4  12.14 

^ 
/ 

19  14  44.39   10.933 

22  20  37.4 

19.50 

6  35.70 

1.076 

19    8    8.69 

18 

19  40  48.58   10.786 

21  26    3.2 

25.90 

9    0.54 

0.928 

19  31  48.04 

14 

19  45    7.09   10.757 

21  15  29.2 

26.92 

9  22.49 

0.900 

19  35  44.60 

15 

19  49  24.91    10.728 

21    4  30.8 

27.93 

9  43.75 

0.871 

19  39  41.16 

IB 

19  53  42.03  10.698 

20  53    8.3 

28.93 

10    4.31 

0.842 

19  43  37.72 

17 

19  57  58.43   10.668 

20  41  22.0 

29.92 

10  24.15 

0.812 

19  47  34.28 

22 

20  19    9.24   10.510 

19  36  45.6 

34.63 

11  52.17 

0.654 

20    7  17.07 

26 

20  35  52.01    10.380 

18  38  31.0 

38.13 

12  48.71 

0.523 

20  23    3.29 

27 

20  40    0.73   10.347 

18  23    5.7 

38.97 

13    0.88 

0.490 

20  26  59.85 

28 

20  44    8.65 

10.314 

18    7  20.4 

39.79 

13  12.24 

0.457 

20  30  56.41 

FEBEUARY. 


2 

21    4  36.28 

10.147 

16  43  47.7 

43.67 

13  57.09 

0.290 

20  50  39.19 

4 

21  12  41.68 

10.079 

16    8  16.7 

45.11 

14    9.37 

0.223 

20  58  32.31 

5 

21  16  43.16 

10.045 

15  50    5.9 

45.79 

14  14.30 

0.189 

21    2  28.86 

6 

21  20  43.84 

10.011 

15  31  38.8 

46.46 

14  18.42 

0.155 

21    6  25.42 

11 

21  40  35.10 

9.844 

13  55  34.2 

49.53 

14  26.91 

0.012 

21  26    8.20 

12 

21  44  30.98 

9.811 

13  35  38.6 

50.09 

14  26.23 

0.045 

21  30    4.75 

21 

22  19  20.52 

9.545 

10  27  12.1 

54.37 

13  46.77 

0.312 

22    5  33.75 

22 

22  23    9.28 

9.519 

10    5  22.5 

54.76 

13  38.98 

0.338 

22    9  30.30 

28 

22  45  49.59 

9.379 

7  51  24.0 

56.79 

12  39.96 

0.477 

22  33    9.63 

MARCH,  1894. 


AT  GREENWICH   APPARENT  NOON. 


^ 

THE    SUN'S 

o 

Sidereal 

Equation 

S 

Time  of 

of  Time, 

n 

Semi- 

to  be 

diameter 

Added  to 

o 

Apparent 

D iff.  for 

Apparent         jDiff.for 

Semi- 

Passing 

Apparent 

Diff.for 

O 

Right  Ascension. 

1  Hour. 

Declination. 

1  Hour. 

diameter. 

Meridian. 

Time. 

1  Hour. 

3 

h     m      s 

22  57    4.55 

9.318 

S.    6°42'34.'l 

57'.57 

16 

9.85 

65!28 

m      s 

12    3.28 

0.537 

4 

23    0  47.94 

9.299 

6  19  29.6 

57.80 

16 

9.60 

65.22 

11  50.16 

0.556 

5 

23    4  30.90 

9.281 

5  56  19.6 

58.02 

16 

9.34 

65.15 

11  36.59 

0.574 

10 

23  22  59.62 

9.201 

3  59  24.9 

58.82 

16 

8.06 

64.87 

10  22.75 

0.654 

11 

23  26  40.28 

9.187 

3  35  51.8 

58.93 

16 

7.81 

64.83 

10    6.89 

0.668 

16 

23  44  59.04 

9.129 

1  37  37.4 

59.24 

16 

6.51 

64.64 

8  43.12 

0.725 

17 

23  48  38.03 

9.121 

1  13  55.5 

59.25 

16 

6.24 

64.61 

8  25.61 

0.734 

18 

23  52  16.83 

9.113 

0  50  13.2 

59.26 

16 

5.98 

64.59 

8    7.90 

0.742 

19 

23  55  55.45 

9.106 

0  26  31.2 

59.24 

16 

5.71 

64.56 

7  50.01 

0.749 

20 

23  59  33.91 

9.099 

S.    0    2  49.6 

59.22 

16 

5.44 

64.54 

7  31.97 

0.755 

21 

0    3  12.24 

9.095 

N.  0  2051.2 

59.18 

16 

5.17 

64.53 

7  13.80 

0.759 

22 

0    6  50.46 

9.091 

0  44  30.8 

59.12 

16 

4.89 

64.51 

6  55.52 

0.763 

24 

0  14    6.70 

9.086 

1  31  45.4 

58.97 

16 

4.34 

64.49 

6  18.74 

0.768 

25 

0  17  44.74 

9.085 

1  55  19.7 

58.88 

16 

4.06 

64.49 

6    0.28 

0.769 

29 

0  32  17.03 

9.090 

3  29    8.9 

58.35 

16 

2.93 

64.49 

4  46.56 

0.764 

30 

0  35  55.23 

9  094 

3  52  27.6  158.181 16 

2.65 

64.50 

4  28.26 

0.761 

Equation 

of  Time, 

to  be 

APRIL. 

Added  to 

Subtracted 

Apparent 
Time. 

1 

0  43  11.92 

9.103 

N.  4  38  52.0 

57.81 

16 

2.08 

64.53 

3  51.94 

0.752 

2 

0  46  50.45 

9.108 

5    1  57.1 

57.60 

16 

1.80 

64.55 

3  33.96 

0.746 

7 

1    5    5.56 

9.146 

6  55  56.1 

56.30 

16 

0.42 

64.  (i8 

2    6.54 

0.708 

8 

1    8  45.18 

9.156 

7  18  24.0 

56.00 

16 

0.15 

64.71 

1  49.65 

0.699 

14 

1  30  48.30 
1  34  29.88 

9.225 
9.239 

9  30  21.9 
9  51  50.1 

53.87 
53.47 

15 

15 

58.56 
58.30 

64.97 
65.03 

0  13.71 

0.630 

15 

0    1.23 

0.616 

25 

2  11  47.24 

9.417 

13  16  38.2 

48.71 

15  55.72 

65.65 

2    9.06 

0.438 

27 

2  19  20.28 

9  460 

13  55  10.4 

47.61 

15  55.22 

65.79 

2  29.08 

0.395 

28 

2  23    7.58 

9.482 

14  14    6.2 

47.04 

15 

54.97 

65.86 

2  38.31 

0.373 

30 

2  30  43.81 

9.528 

14  51  15.9 

45.86 

15 

54.47 

66.01 

2  55.15 

0.328 

MARCH,  1894. 


AT  GREENWICH   MEAN   NOON. 


, 

THE 

SUN'S 

r 

Equation 

Sidereal 

^ 

of  Time, 

Time, 

^ 

to  be 

or 

z. 

Subtracted 

Right  Ascension 

~ 

Apparent 

Diff. for 

Apparent 

Diff.  for 

from 

Diff.  for 

of 

c 

Right  Ascension. 

1  Hour. 

Declination. 

1  Hour. 

Mean  Time. 

1  Hour. 

Mean  Sun. 

h     m       s 

s 

1 

m       s 

s 

h     m      .s 

3 

22  57    2.68 

9.319 

S.   6  42  45;8  '  57.58 

12    3.39 

0.537 

22  44  59.29 

4 

23    0  46.11 

9.300 

6  19  41.0    57.81 

11  50.27 

0.556 

22  48  55.84 

5 

23    4  29.11 

9.282 

5  56  30.9    58.02 

11  36.71 

0.574 

22  52  52.40 

10 

23  22  58.04 

9.203 

3  59  35.1     58.83 

10  22.87 

0.654 

23  12  35.17 

11 

23  26  38.73 

9.189 

3  36    1.8    58.94 

10    7.01 

0.668 

23  16  31.72 

16 

23  44  57.71 

9.131 

1  37  46.1 !  59.25 

8  43.22 

0.725 

23  36  14.49 

17 

23  48  36.75 

9.123 

1  14    3.8!  59.27 

8  25.71 

0.734 

23  40  11.04 

18 

23  52  15.60 

9.115 

0  50  21.3    59.27 

8    8.00 

0.742 

23  44    7.60 

19 

23  55  54.26 

9.108 

0  26  39.0    59.26 

7  50.11 

0.749 

23  48    4.15 

20 

23  59  32.77 

9.101 

S.  0    2  57.1  1  59.23 

7  32.06 

0.755 

23  52    0.70 

21 

0    3  11.15 

9.096 

N.  0  20  44.0  i  59.19 

7  13.89 

0.760 

23  55  57.26 

22 

0    6  49.41 

9.093 

0  44  24.0 

59.14 

6  55.60 

0.764 

23  59  53.81 

24 

0  14    5.74 

9.088 

1  31  39.2 

58.99 

6  18.82  \  0.768 

0    7  46.92 

25 

0  17  43.84 

9.087 

1  55  13.8 

58.89 

6    0.36  [  0.769 

0  11  43.47 

29 

0  32  16.31 

9.092 

3  29    4.3 

58.37 

4  46.62 

0.764 

0  27  29.69 

30 

0  35  54.56 

9.096 

3  52  23.2 

58.20 

4  28.31 

0.761 

0  31  26.24 

Equation 

of  Time, 

to  be 

APRIL. 

Subtracted 
from 

Ad<led  to 

0  43  11.34 

9.105 

Mean  Time. 

1 

N.  4  38  48.3 

57.83 

3  51.99 

0.752 

0  39  19.35 

2 

0  46  49.91 

9.110 

5    1  53.6 

57.62 

3  34.01 

0:746 

0  43  15.90 

7 

1    5    5.23 

9.148 

6  55  54.1 

56.32 

2    6.56 

0.708 

1    2  58.67 

8 

1    8  44.90 

9.158 

7  18  22.3 

56.02 

1  49.67 

0.699 

1    6  55.23 

14 

1  30  48.27 
1  34  29.88 

9.227 
9.241 

9  30  21.7 
9  51  50.1 

53.88 
53.48 

0  13.72 

0.630 
0.616 

1  30  34.55 

15 

0    1.23 

1  34  31.11 

25 

2  11  47.58 

9.419 

13  16  39.9 

48.72 

2    9.08 

0.438 

2  13  56.66 

27 

2  19  20.67 

9.461 

13  55  12.3 

47.62 

2  29.10 

0.395 

2  21  49.77 

28 

2  23    8.00 

9.483 

14  14    8.3 

47.05 

2  38.32 

0.373 

2  25  46.32 

30 

2  30  44.27 

9.528 

14  51  18.2 

45.86 

2  55.16 

0.328 

2  33  39.44 

MAY,  1894. 

AT   GREENWICH   APPARENT   NOON. 

c 
o 

THE   RUN'S 

Sidereal 

Equation 
of  Time, 

Time  of 

to  be 

^ 

Semi- 

Subtracted 

^ 

diameter 

from 

O 
1 

Apparent 
Right  Ascension. 

Diff.  for 
1  Hour. 

Apparent 
Declination. 

Diff .  for 
1  Hour. 

Semi- 
diameter. 

Passing 
Meridian 

Apparent 
Time. 

Diff.  for 
1  Hour. 

1 

li     m       s 

2  34  32.74 

9^551 

N.15°  9  29.0 

45!24 

15  54!23 

66'.09 

m       s 

3    2.75 

0.305 

2 

2  38  22.22 

9.574 

15  27  27.2 

44.61 

15  53.99 

66.17 

3    9.80 

0.282 

16 

3  32  54.00 

9.900 

19    9  51.6 

34.41 

15  51.04 

67.30 

3  49.71 

0.044 

17 

3  36  51.89 

9.923 

19  23  27.7 

33.59 

15  50.85 

67.38 

3  48.38 

0.067 

19 

3  44  49.31 

9.969 

19  49  40.6 

31.93 

15  50.49 

67.54 

3  44.08  i  0.112 

20 

3  48  48.85 

9.992 

20    2  16.8 

31.08 

15  50.30 

67.62 

3  41.12 

0.135 

21 

3  52  48.93 

10.015 

20  14  32.6 

30.22 

15  50.12 

67.70 

3  37.60 

0.158 

22 

3  56  49.55 

10.037 

20  26  27.7 

29.35 

15  49.95 

67.78 

3  33.55 

0.180 

23 

4    0  50.71 

10.059 

20  38    1.9 

28.48 

15  49.77 

67.85 

3  28.96 

0.202 

27 

4  17    0.58 

10.145 

21  20  45.1 

24.88 

15  49.10 

68.12 

3    5.38 

0.288 

28 

4  21    4.31 

10.165 

21  30  31.3 

23.96 

15  48.94 

68.19 

2  58.24 

0.308 

31 

4  33  18.31 

10.222 

21  57  35.5 

21.14 

15  48.49 

68.37 

2  33.98 

0.365 

JUNE. 

Equation 

of  Time, 

to  be 

Subtracted 

from 

Added  to 

Apparent 

Time. 

1 

4  37  23.85 

10.240 

N.22    5  51.4 

20.18 

15  48.35 

68.43 

2  25.02 

0.382 

2 

4  41  29.81 

10.256 

22  13  44.1 

19.21 

15  48.22 

68.48 

2  15.64 

0.398 

3 

4  45  36.15 

10.272 

22  21  13.6 

18.24 

15  48.09 

68.53 

2    5.89 

0.414 

4 

4  49  42.86 

10.287 

22  28  19.6 

17.26 

15  47.96 

68.58 

1  55.77 

0.429 

10 

5  14  29.52 

10.355 

23    2  34.7 

11.25 

15  47.32 

68.82 

0  48.64 

0.497 

11 

5  18  38.14 

10.363 

23    6  52.6 

10.23 

15  47.23 

68.85 

0  36.61 

0.505 

12 

5  22  46.95 

10.370 

23  10  46.0 

9.21 

15  47.14 

68.88 

0  24.39 

0.512 

13 

5  26  55.93 ' 
5  31    5  04; 

10.377 
10.382 

23  14  14.9 
23  17  19.3 

8.19 

7.17 

15  47.06 
15  46.98 

68.90 
68.91 

0  12.00 

0.518 

14 

0    0.52 

0.524 

15 

5  35  14.28 

10.387 

23  19  59.0 

6.14 

15  46.90 

68.93 

0  13.16 

0.529 

24 

6  12  39.62 

10.392 

23  25  23.9 

3.15 

15  46.36 

68.95 

2    9.15 

0.534 

26 

6  20  58.23 ' 

10.383 

23  22    3.8 

5.20 

15  46.28 

68.91 

2  34.58 

0.526 

27 

6  25    7.37 

10.377 

23  19  46.8 

6.23 

15  46.25 

68.89 

2  47.12 

0.519 

28 

6  29  16.34 

10.370 

23  17    5.1 

7.25 

15  46.22 

68.86 

2  59.50 

0.512 

30 

6  37  33.76 ' 

10.354 

23  10  28.1 

9.29 

15  46.18 

68.81 

3  23.73 

0.495 

MAY,  1894. 


AT  GREENWICH   MEAN   NOON. 


.= 

THE 

SUN'S 

c 

Sidereal 

't 

Equation 
of  Time, 

Time, 

Xi 

or 

o 

Apparent 

Diff.  for 

Apparent 

Diff.  for 

to  be 
Added  to 

Diff.  for 

Right  Ascension 
of 

Right  Ascension. 

1  Hour. 

Declination. 

1  Hour. 

Mean  Time. 

1  Hour. 

Mean  Sun. 

h     m        s        j       s 

m       s 

s 

h      m       s 

1 

2  34  33.22 

9.551 

N.  15'  9  31.3 

45.'24 

3    2.77 

0.305 

2  37  35.99 

2 

2  38  22.73 

9.574 

15  27  29.6 

44.61 

3    9.821  0.282 

2  41  32.55 

16 

3  32  54.64 

9.900 

19    9  53.9 

34.41 

3  49.70 

0.044 

3  36  44.34 

17 

3  36  52.52 

9.923 

19  23  29.9 

33.59 

3  48.38 

0.067 

3  40  40.90 

19 

3  44  49.93 

9.969 

19  49  42.6 

31.93 

3  44.08 

0.112 

3  48  34.01 

20 

3  48  49.46  1    9.992 

20    2  18.7 

31.08 

3  41.11 

0.135 

3  52  30.57 

21 

3  52  49.53 

10.015 

20  14  34.4 

30.22 

3  37.59 

0.158 

3  56  27.13- 

22 

3  56  50.15 

10.037 

20  26  29.5 

29.35 

3  33.54 

0.180 

4    0  23.68. 

23 

4    0  51.29 

10.059 

20  38    3.6 

28.48 

3  28.95 

0.202 

4    4  20.24 

27 

4  17    1.11 

10.144 

21  20  46.4 

24.88 

3    5.37 

0.288 

4  20    6.47 

28 

4  21    4.81 

10.164 

21  30  32.5 

23.96 

2  58.22 

0.308 

4  24    3.03 

31 

4  33  18.74 

10.221 

21  57  36.4 

21.14 

2  33.96 

0.365 

4  35  52.71 

Equation 
of  Time, 

to  be 
Added  to 

JUIN 

E. 

Subtracted 

from 

N.22    5  52.2 

20.18 

Mean  Time. 

0.382 

1 

4  37  24.26 

10.239 

2  25.00 

4  39  49.27 

2 

4  41  30.20 

10.255 

22  13  44.9 

19.21 

2  15.63 

0.398 

4  43  45.82 

3 

4  45  36.51 

10.271 

22  21  14.3 

18.24 

2  ^5.87 

0.414 

4  47  42.38 

4 

4  49  43.19 

10.286 

22  28  20.2 

17.26 

1  55.75 

0.429 

4  51  38.94 

10 

5  14  29.66 

10.354 

23    2  34.9 

11.25 

0  48.63 

0.497 

5  15  18.29 

11 

5  18  38.25 

10.362 

23    6  52.7 

10.23 

0  36.60 

0.505 

5  19  14.85 

12 

5  22  47.03 

10.369 

23  10  46.1 

9.21 

0  24.38 

0.512 

5  23  11.41 

13 

5  26  55.97 
5  31    5.04 

10.376 
10.381 

23  14  15.0 
23  17  19.3 

8.19 
7.17 

0  12.00 

0.518 
0.524 

5  27    7.97 

14 

0    0.52 

5  31    4.53 

15 

5  35  14.24 

10.385 

23  19  59.0 

6.14 

0  13.16 

0.529 

5  35    1.09 

24 

6  12  39.25 

10.390 

23  25  24.0 

3.14 

2    9.13 

0.534 

6  10  30.12 

26 

6  20  57.79 

10.381 

23  22    4.0 

5.19 

2  34.56 

0.526 

6  18  23.23 

27 

6  25    6.88 

10.375 

23  19  47.0 

6.22 

2  47.09 

0.519 

6  22  19.79 

28 

6  29  15.83 

10.368 

23  17    5.4 

7.25 

2  59.48 

0.512 

6  26  16.35 

30 

6  37  33  17 

10.352 

23  10  28.6 

9.29 

3  23.70 

0.495 

6  34    9.47 

JULY,  1894. 


AT   GREENWICH   APPARENT    NOON. 

^ 

THE    SUN'S 

o 

Sidereal 

Equation 

S 

Time  of 

of  Time, 

Xi 

Semi- 

to  be 

diameter 

Added  to 

o 

Apparent 

Diff.  for 

Apparent 

Diff.  for 

Semi- 

Passing 

Apparent 

Diff.  for 

Q 

Right  Ascension. 

1  Hour. 

Declination. 

1  Hour. 

diameter. 

Meridian 

Time. 

1  Hour. 

h    m        s 

s 

s 

m       s 

s 

1 

6  41  42.14 

10.344 

N.23°   6  33.0 

10.30 

15  46.17 

68.77 

,3  35.52 

0.486 

2 

6  45  50.27 

10.333 

23    2  13.6 

11.31 

15  46.16 

68.73 

3  47.06 

0.475 

10 

7  18  43.28 

10.209 

22  13  19.1 

19.18 

15  46.31 

68.34 

5    7.39 

0.352 

11 

7  22  48.08 

10.190 

22    5  27.3 

20.13 

15  46.35 

68.28 

5  15.60 

0.333 

12 

7  26  52.42 

10.170 

21  57  12.8 

21.08 

15  46.39 

68.22 

5  23.36 

0.313 

20 

7  59    8.89 

9.998 

20  38    3.5 

28.30 

15  46.87 

67.63 

6    7.25 

0.141 

21 

8    3    8.55 

9.975 

20  26  33.8 

29.16 

15  46.95 

67.55 

6  10.35 

0.118 

24 

8  15    4.20 

9.904 

19  50    2.2 

31.70 

15  47.19 

67.31 

6  16.30 

0.048 

30 

8  38  40.00 

9.758 

18  28    9.1 

36.47 

15  47.79 

66.80 

6  12.77 

0.098 

31 

8  42  33.90     9.733 

18  13  24.7  1  37.22 

15  47.91 

66.71 

6  10.12 

0.123 

AUGUST. 

Equation 
of  Time, 

to  be 
Added  to 

Subtracted 
from 

Apparent 

66.62 

Time. 

1 

8  46  27.20 

9.708 

N.  17  58  22.4 

37.96 

15  48.03 

6    6.87 

0.148 

2 

8  50  19.89 

9.683 

17  43    2.4 

38.69 

15  48.16 

66.54 

6    3.01 

0.173 

6 

9    5  44.53 

9.581 

16  38  52.3 

41.48 

15  48.73 

66.20 

5  41.49 

0.275 

7 

9    9  34.16 

9.555 

16  22    8.8 

42.14 

15  48.88 

66.11 

5  34.58 

0.300 

8 

9  13  23.18 

9.530 

16    5    9.6 

42.79 

15  49.04 

66.03 

5  27.07 

0.325 

9 

9  17  11.61 

9.505 

15  47  55.0 

43.43 

15  49.20 

65.94 

5  18.96 

0.350 

10 

9  20  59.48 

9.480 

15  30  25.3 

44.05 

15  49.36 

65.86 

5  10.25 

0.375 

12 

9  28  33.32 

9.432 

14  54  41.8 

45.26 

15  49.70 

65.70 

4  51.08 

0.423 

13 

9  32  19.41 

9.409 

14  36  28.7 

45.84 

15  49.88 

65.62 

4  40.64 

0.447 

14 

9  36    4.93 

9.386 

14  18    1.6 

46.41 

15  50.05 

65.54 

4  29.64 

0.470 

15 

9  39  49.92 

9.363 

13  59  21.0 

46.96 

15  50.23 

65.46 

4  18.10 

0.492 

18 

9  51    1.73 

9.299 

13    2    0.5 

48.58 

15  50.78 

65.24 

3  40.35 

0.556 

19 

9  54  44.66 

9.279 

12  42  28.4 

49.09 

15  50.97 

65.17 

3  26.76 

0.576 

20 

9  58  27.13 

9.260 

12  22  44.2 

49.59 

15  51.16 

65.10 

3  12.71 

0.595 

21 

10    2    9.13 

9.241 

12    2  48.2 

50.08 

15  51.35 

(55.03 

2  58.20 

0.614 

22 

10    5  50.69 

9.223 

11  42  40.6 

50.55 

15  51.54 

64.96 

2  43.24 

0.632 

27 

10  24  12.30 

9.140 

9  59  20.2 

52.73 

15  52.56 

64.66 

1  22.31 

0.714 

JULY,  1894. 


AT   GREENWICH   MEAN   NOON. 


, 

THE 

SUN'S 

o 

Equation 

Sidereal 

s 

of  Time, 

Time, 

to  be 

or 

^ 

Subtracted 

Right  Ascension 

^ 

Apparent 

Diff.  for 

Apparent 

Diff.  for 

from 

Diff.  for 

of 

1 

Right  Ascension. 

1  Hour. 

Declination. 

1  Hour. 

Mean  Time. 

1  Hour. 

Mean  Sun. 

h     m       s 

^ 

ra       s 

s 

h     m       s 

1 

6  41  41.52 

10.343 

N.  23°   6  33.6 

10.30 

3  35.49 

0.486 

6  38    6.03 

2 

6  45  49.61 

10.332 

23    2  14.2 

11.31 

3  47.03 

0.475 

6  42    2.59 

10 

7  18  42.41 

10.208 

22  13  20.7 

19.18 

5    7.36 

0.3.52 

7  13  35.06 

11 

7  22  47.19 

10.189 

22    5  29.1 

20.13 

5  15.58 

0.333 

7  17  31.61 

12 

7  26  51.51 

10.169 

21  57  14.7 

21.07 

5  23.33 

0.313 

7  21  28.17 

20 

7  59    7.87 

9.997 

20  38    6.3 

28.29 

6    7.24 

0.141 

7  53    0.64 

21 

8    3    7.53 

9.974 

20  26  36.8 

29.16 

6  10.33 

0.118 

7  56  57.19 

24 

8  15    3.16 

9.904 

19  50    5.4 

31.70 

6  16.30 

0.048 

8    8  46.87 

30 

8  38  38.99 

9.759 

18  28  12.8 

36.47 

6  12.78 

0.098 

8  32  26.21 

31 

8  42  32.90 

9.734 

IS  13  28.5 

37.22 

6  10.13 

0.123 

8  36  22.77 

Equation 
of  Time, 

to  be 

AUdU 

ST. 

Subtracted 
from 

Adde.i  to 

8  46  26.21 

9.709 

N.  17  58  26.2 

37.96 

Mean  Time. 

0.148 

1 

6    6.88 

8  40  19.32 

2 

8  50  18.91 

9.684 

17  43    6.2 

38.69 

6    3.03    0.173 

8  44  15.88 

(> 

9    5  43.62 

9.582 

16  38  56.1 

41.48 

5  41.51  1  0.275 

9    0    2.11 

7 

9    9  33.27 

9.556 

16  22  12.6 

42.14 

5  34.61  1  0.300 

9    3  58.66 

8 

9  13  22.32 

9.531 

16    5  13.4 

42.79 

5  27.10;  0.325 

9    7  55  22 

9 

9  17  10.76 

9.506 

15  47  58.8 

43.43 

5  18.99    0.350 

9  1151.78 

10 

9  20  58.61 

9.481 

15  30  29.0 

44.05 

5  10.28    0.375 

9  15  48.33 

12 

9  28  32.56 

9.433 

14  54  45.4 

45.26 

4  51.11     0.423 

9  23  41.44 

13 

9  32  18.67 

9.410 

14  36  32.2 

45.84 

4  40.67    0.447 

9  27  38.00 

14 

9  36    4.23 

9.387 

14  18    5.0 

46.41 

4  29.67    0.470 

9  31  34.56 

15 

9  39  49.25 

9.364 

13  59  24.3 

46.97 

4  18.14    0.492 

9  35  31.11 

18 

9  51    1.16 

9  301 

13    2    3.4 

48.59 

3  40.38 !  0.556 

9  47  20.78 

19 

9  54  44.13 

9.280 

12  42  31.2 

49.10 

3  26.80    0  576 

9  51  17.33 

20 

9  58  26.63 

9.2(il 

12  22  46.8 

49.(i0 

3  12.74    0.595 

9  55  13.89 

21 

10    2    8.67 

9.243 

12    2  50.6 

50.09 

2  58.23    0.614 

9  59  10.44 

22 

10    5  50.27 

9.225 

11  42  42.8 

50.5ti 

2  43.27    0.632 

10    3    7.00 

27 

10  24  12.10 

9.142 

9  59  21.3 

52.74 

1  22.32    0.714 

10  22  49.77 

SEPTEMBER,  1894. 


AT    GREENWICH   APPARENT   NOON. 


THE    SUN'S 

j: 

Equation 

c 

Sidereal 

of  Time 

c 

Time  of 

to  be 

"^ 

Semi- 

Subtracted 

,s 

diameter 

from 

Diff. 

"o 

Apparent 

Diff.  for 

Apparent 

Diff.  for 

Semi- 

Passing 

Apparent 

for 

Right  Ascension. 

1  Hour. 

Declination. 

1  Hour. 

diameter. 

Meridian. 

Time. 

1  Hour. 

h     m         s 

s 

s 

m        s 

s 

1 

10  42  24.83 

9.071 

N.  8  11  59.1 

54.'56 

15  53'. 67 

64.41 

0    7.70 

0.783 

2 

10  46    2.39 

9.059 

7  50    5.8 

54.89 

15  53.90 

64.37 

0  26.64 

0.795 

3 

10  49  39.66 

9.047 

7  28    4.9155.19 

15  54.14 

64.33 

0  45.87 

0.807 

15 

11  32  50.86 

8.968 

2  56    9.1  1  57.79 

15  57.17 

64.08 

4  52.64 

0.886 

16 

11  36  26.07 

8.967 

2  33    0.4    57.93 

15  57.43 

64.07 

5  13.92 

0.887 

22 

11  57  57.98 

8.982 

N.  0  13  14.9  :  58.46 

15  58.99 

64  11 

7  20.99 

0.872 

23 

12    1  33.62 

8.988 

S.   0  10    8.6    58.50 

15  59.26 

64.13 

7  41.84 

0.866 

24 

12    5    9.41 

8.995 

0  33  32.8    58.52 

15  59.52 

64.15 

8    2.56 

0.859 

25 

12    8  45.36 

9.002 

0  56  57.6  1  58  53 

15  59.79 

64.17 

8  23.10 

0.852 

26 

12  12  21.50 

9.010 

1  20  22.3  I  58.53 

16    0.05 

64.20 

8  43.46 

0.844 

27 

12  15  57.84 

9.019 

1  43  46.8    58.51 

16    0.32 

64.23 

9    3.62 

0.835 

30 

12  26  48.26 

9.050 

2  53  54.6 

58.34 

16    1.15 

64.34 

10    2.70 

0.805 

OCTOBER. 


12  30 
12  41 

12  44 

13  44 
13  48 

13  59 

14  3 
14  18 
14  22 


25.58 

9.062 

19.36 

9.101 

57.94 

9.116 

18.12 

9.465 

5.61 

9.493 

32.34 

9.583 

22.71 

r,.614 

51.76 

9.742 

45.96 

9.775 

3  17  14.0 

4  26  57.6 
4  50  6.0 

10  47  51.1 

11  9  7.6 

12  11  56.1 

12  32  30.5 

13  52  48.0 

14  12  20.1 


58.26 
57.91 
57.77 
53.39 
53.00 
51.67 
51 .20 
49.12 
48.55 


1.42 
2.26 
2.55 
6.95 
7.21 
7.98 
8.24 
9.26 
9.52 


64.38 
64.52 
64.58 
65.81 
65.90 
(i6.20 
66.31 
(',6.74 
66.85 


10  21.88 

11  17.61 
11  35.53 
15  19.61 
15  28.65 
15  51  52 

15  57.69  

1()  14.80  0.114 

16  17.16  0.082 


0.793 
0.754 
0.739 
0.390 
0.362 
0.272 
0.241 


SEPTEMBER,  18U4. 


AT   GREENWICH   MEAN    NOON. 


THE 

SUN'S 

c 

Sidereal 

_£ 

Equation 
of  Time, 

Time, 

or 

to  be 

Right  Ascension 

o 

Apparent 

Diff .  for 

Apparent 

Diff.  for 

Added  to 

Diff.  for 

of 

>> 

Right  Ascension. 

1  Hour. 

Declination. 

1  Hour. 

Mean  Time. 

1  Hour. 

Mean  Sun. 

h    m       s 

s 

m        s 

s 

h     m      s 

1 

10  42  24.85 

9.073 

N.  8  li  58.9 

54.57 

0    7.70 

0.783 

10  42  32.55 

2 

10  46    2.45 

9.061 

7  50    5.3 

54.90 

0  26.65 

0.795 

10  46  29.10 

3 

10  49  39.77 

9.049 

7  28    4.1 

55.20 

0  45.88 

0.807 

10  50  25.66 

15 

11  32  51.59 

8.970 

2  56    4.3 

57.81 

4  52.71 

0.887 

11  37  44.30 

16 

11  36  26.86 

8.969 

2  32  55.2 

57.94 

5  14.00 

0.887 

11  41  40.86 

22 

11  57  59.08 

8.984 

N.  0  13    7.7 

58.47 

7  21.10 

0.872 

12    5  20.18 

23 

12    1  34.78 

8.990 

S.    0  10  16.2 

58.51 

7  41.96 

0.866 

12    9  16.73 

24 

12    5  10.61 

8.997 

0  33  40.7 

58.53 

8    2.67 

0.859 

12  13  13.29 

25 

12    8  46.62 

9.004 

0  57    5.8 

58.54 

8  23.22 

0.852 

12  17    9.84 

26 

12  12  22.81 

9.012 

1  20  30.8 

58.54 

8  43.58 

0.844 

12  21    6.39 

27 

12  15  59.20 

9.021 

1  43  55.6 

58.52 

9    3.75 

0.835 

12  25    2.95 

30 

12  26  49.77 

9.052 

2  54    4.4 

58.35 

10    2.84 

0.805 

12  36  52.61 

OCTOBER. 


1 

12  30  27.15 

9.063 

S.  3  17  24.1 

58.28 

10  22.01 

0.793 

12  40  49.16 

4 

12  41  21.07 

9.102 

4  27    8.6 

57.93 

11  17.75 

0.754 

12  52  38.82 

5 

12  44  59.70 

9.117 

4  50  17.2 

57.78 

11  35.67 

0.739 

12  56  35.38 

21 

13  44  20.54 

9.46('. 

10  48    4.7 

53.39 

15  19.71 

0.390 

13  59  40.24 

22 

13  48    8.06 

9.494 

11    9  21.3 

52.99 

15  28.74 

0.362 

14    3  36.80 

25 

13  59  34.87 

9.584 

12  12    9.7 

51.66 

15  51.59 

0.272 

14  15  26.46 

26 

14    3  25.27 

9.615 

12  32  44.1 

51.19 

15  57.75 

0.241 

14  19  23.02 

30 

14  18  54.40 

9.743 

13  53    1.3 

49.11 

16  14.84 

0.114 

14  35    9.24 

31 

14  22  48.62 

9.775 

14  12  33.3 

48.55 

16  17.18 

0.081 

14  39    5.80 

NOVEMBER,  1894. 


AT   GREENWICH   APPARENT   NOON, 


o 

THE    SUN'S 

Sidereal 

Equation 
of  Time, 

IS 

Time  of 

to  be 

^ 

Semi- 

Subtracted 

■*^ 

diameter 

from 

c 

Apparent 

Diff.  for 

Apparent 

Diff.  for 

Semi- 

Passing 

Apparent 

Diff.  for 

1 

Right  Ascension. 

1  Hour. 

Declination. 

1  Hour. 

diameter. 

Meridian. 

Time. 

1  Hour. 

1 

h     m       s 

14  26  40.95 

9.808 

S.14°3138!6 

47.97 

16    9!77 

66.97 

m       s 

16  18.74 

0.049 

2 

14  30  36.72     9.841 

14  50  42.8 

47.37 

16  10.02 

67.08 

16  19.50 

0.016 

4 

14  38  30.681    9.907 

15  28    7.2 

46.12 

16  10.52 

67.31 

16  18.66 

0.051 

5 

14  42  28.87     9.941 

15  46  26.5 

45.48 

16  10.77 

67.43 

16  17.04 

0.085 

6 

14  46  27.87 

9.975 

16    4  30.0 

44.81 

16  11.02 

67.55 

16  14.59 

0.119 

10 

15    2  32.13 

10.114 

17  13  58.1 

41.98 

16  11.96 

68.03 

15  56.61 

0.257 

11 

15    6  35.29 

10.149 

17  30  36.7 

41.23 

16  12.19 

68.15 

15  50  02 

0.292 

12 

15  10  39.29 

10.184 

17  46  57.2 

40.47 

16  12.41 

68.27 

15  42.60 

0.327 

20 

15  43  41.92 

10.467 

19  46    4.1 

33.80 

16  14.04 

69.19 

14  12.67 

0.609 

21 

15  47  53.56 

10.502 

19  59  24.6  32.90 

16  14.23 

69.30 

13  57.64 

0.643 

22 

15  52    6.01 

10.536 

20  12  23.4  31.98 

16  14.41 

69.41 

13  41.79 

0.677 

Equation 

of  Time, 

to  be 

Subtracted 

DECEMBEE. 

from 

Added  to 

70.29 

Apparent 
Time. 

1 

16  30  32.50 

10.809 

S.  21  51  47.6 

23.05 

16  15.92 

10  44.80 

0.949 

2 

16  34  52.22 

10.834 

22    0  48.1 

21.99 

16  16.07 

70.38 

10  21.70 

0.974 

5 

16  47  54.88 

10.904 

22  25  15.7 

18.75 

16  16.51 

70.61 

9    8.92 

1.045 

6 

16  52  16.84 

10.925 

22  32  32.6 

17.65 

16  16.65 

70.68 

8  43.58 

1.066 

13 

17  23    3.08 

11.044 

23  10  59.7 

9.75 

16  17.46 

71.08 

5  33.77 

1.184 

14 

17  27  28.30 

11.056 

23  14  39.9 

8.60 

16  17.55 

71.12 

5    5.19 

1.196 

20 

17  54    4.59 

11.106 

23  26  53.9 

1.58 

16  17.96 

71.26 

2    8.74 

1.246 

21 

17  58  31.19 

11.109 

23  27  17.6 

0.40 

16  18.03 

71.26 

1  38.78 

1.249 

22 

18    2  57.84 

11.111 

23  27  13.0 

0.78 

16  18.0S 

71.27 

1    8.78 

1.251 

23 

18    7  24.52 

11.111 

23  26  40.0 

1.96 

16  18.13 

71.27 

0  38.74 

1.251 

24 

18  n  51.18 
18  16  17.79 

11.110 
11.107 

23  25  38.7 
23  24    9.1 

3.14 
4.32 

16  18.17 
16  18.20 

71.26 
71.25 

0    8.72 

1.250 

25 

0  21.26 

1.247 

NOVEMBEE,  18!U. 


AT  GREENWICH   MEAN   MOON. 


J3 

THE 

^UN'S 

o 

Sidereal 

Equation  of 
Time, 

Time, 

J3 

or 

z 

to  be 

Right  Ascension 

? 

Apparent 

Diff.  for 

Apparent 

Diff.  for 

Added  to 

Diff.  for 

of 

S 

Right  Ascension. 

1  Hour. 

Declination. 

1  Hour. 

Mean  Time.     1  Hour. 

Mean  Sun. 

h     m       s 

8 

m       s 

s 

h    m        s 

1 

14  26  43.61 

9.808 

S.14  3l'5i'.6 

47.97 

16  18.74 

0.048 

14  43    2.35 

2 

14  30  39.40 

9.841 

14  50  55.7 

47.37 

16  19.51 

0.015 

14  46  58.91 

4 

14  38  33.38 

9.907 

15  28  19.8 

46.12 

16  18.64 

0.051 

14  54  52.02 

5 

14  42  31.57  i    9.941 

15  46  38.8 

45.47 

16  17.01 

0.085 

14  58  48.58 

6 

14  46  30.57  1    9.975 

16    4  42.1 

44.80 

16  14.56 

0.119 

15    2  45.13 

10 

15    2  34.82 

10.114 

17  14    9.2 

41.97 

15  56.54 

0.257 

15  18  31.36 

11 

15    6  37.97 

10.149 

17  30  47.5 

41.22 

15  49.94 

0.292 

15  22  27.91 

12 

15  10  41.96 

10.184 

17  47    7.8 

40.46 

15  42.51 

0.327 

15  26  24.47 

20 

15  43  44.40 

10.466 

19  46  12.0 

33.79 

14  12.53    0.609 

15  57  56.93 

21 

15  47  56.00 

10.500 

19  59  32.3 

32.89 

13  57.49  1  0.644 

16    1  53.49 

22 

15  52    8.41 

10.534 

20  12  30.6 

31.97 

13  41.63 

0.678 

16    5  50.04 

Equation 

of  Time, 

to  be 

Added  to 

DECEMI 

S.21  51  51.7 

3EE. 

23.04 

Sul)tracted 

from 
Mean  Time. 

1 

16  30  34.44 

10.806 

10  44. ('.3 

0.949 

16  41  19.06 

2 

16  34  54.09 

10.831 

22    0  51.9 

21.98 

10  21.53    0.974 

16  45  15.62 

5 

16  47  56.54 

10.901 

22  25  18.5 

18.74 

9    8.76 

1.045 

16  57    5.30 

6 

16  52  18.43 

10.922 

22  32  35.2 

17.64 

8  43.43 

1.066 

17    1     1.86 

13 

17  23    4.11 

11.040 

23  11    0.6 

9.74 

5  33.66 

1.184 

17  28  37.77 

14 

17  27  29.24 

11.052 

23  14  40.6 

8.59 

5    5.09 

1.196 

17  32  34.33 

20 

17  54    5.00 

11.102 

23  26  53.9 

1.58 

2    8.69 

1.245 

17  56  13.68 

21 

17  58  31.49 

11.105 

23  27  17.6 

0.40 

1  38.75     1.249 

18    0  10.24 

22 

18    2  58.05 

11.107 

23  27  13.0 

0.78 

1    8.75     1.251 

18    4    6.80 

23 

18    7  24.63 

11.107 

23  26  40.0 

1.96 

0  38.73     1.251 

18    8    3.36 

24 

18  11  51.20 
18  16  17.73 

11.106 
11.103 

23  25  38.7 
23  24    9.1 

3.14 
4.32 

0    8.72 

1.250 
1.247 

18  11  59.92 

25 

0  21.25 

18  15  56.48 

VENUS,  1894. 


GREENWICH   MEAN   TIME. 


JANUARY. 

MAY. 

.a 
c 
o 

o 

1 

Apparent 

Right 
Ascension. 

Var.  of 

R.  A. 

for 

1  Hour. 

Apparent 
Declination. 

Var.  of 

Decl. 

for 

IHour. 

Meridian 
Passage. 

0 
0 
p 

Apparent 

Right 
Ascension. 

Var.  of 

R.  A. 

for 

1  Hour. 

Apparent 
Declination. 

Var.  of 

Decl. 

for 

1  Hour. 

Meridian 
Passage. 

Noon. 

Noon. 

Noon. 

Noon. 

Noon. 

Noon. 

Noon. 

Noon. 

25 

26 
27 

28 

h    m      s 
22  23  39.23 
22  23  23.60 
22  22  58.71 
22  22  24.53 

—0.461 
0.844 
1.230 
1.617 

— 5°2d46'.8 
5    7  14.1 
4  54  31.5 
4  42  41.5 

+34  87 
32.83 
30.69 
28.45 

h    m 
2    42 
2    0.0 
155.6 
151.1 

21 
22 
23 

24 

h    m     s 
1    1  17.91 
1    5  22.29 
1    9  27.48 
1  13  33.50 

+  10.165 
10.199 
10.233 
10.268 

+4°  28  47.9 

4  51  31.6 

5  14  18.8 
5  37    8.7 

+56.74 
56.89 
57.02 
57.12 

h    m 
21    5.0 
21    5.1 
21    5.2 
21    5.4 

Day  of  the  Month..., 

1st 

6th 

11th 

16th 

21st 

26th 

31st 

Day  of  the  Month 

1st 

6th 

nth 

16th 

21st 

26th 

31st 

Semidiameter 

Hor.  Parallax 

17:7 
18.4 

19:1 

19.8 

2d!7 
21.4 

22:4 

23.2 

24'2 
25.1 

26!  1 
27.1 

28  !0 
29.0 

Semidiameter 

Hor.  Parallax 

ll!8  H".2 
12.211.6 

l6'.7 
11.0 

id!2 
10.5 

9'.7 
10.0 

9.3 
9.6 

8:9 
9.2 

MARS,  1894. 


GREENWICH   MEAN   TIME. 


JANUARY. 

MARCH. 

5 

Apparent 

Right 
Ascension. 

Var.  of 

R.  A. 

for 

IHour. 

Apparent 
Declination. 

Var.  of 

Decl. 

for 

1  Hour. 

Meridian 
Passage. 

c 
c 

0 

1 

Apparent 

Right 
Ascension. 

Var.  of 

R.  A. 

for 

1  Hour. 

Apparent 
Declination. 

Var.  of 

Decl. 

for 

1  Hour, 

Meridian 
Passage. 

1 

Noon. 

Noon. 

Noon. 

Noon. 

Noon. 

N'on. 

Noon. 

Noon. 

14 
15 
16 
17 

h    m      s 
16  29  56.16 
16  32  .50.64 
16  35  45.48 
16  38  40.69 

+7^262 
7.278 
7.293 
7.308 

— 21°41  34.9 

21  48  25.9 
2155    5  8 

22  134.6 

— 17'.35 
16.89 
16.43 
15.97 

h    m 
20  53.3 
20  52.3 
20  51.2 
20  50.2 

1  h    m     s 
28,20    9  47.12 

29  20  12  45.54 

30  20  15  43.68 

31  20  18  41.53 

+7.440 
7.429 
7.417 
7.405 

-21    5  25.4 
20  57  23  0 
20  49    9.8 
20  40  45.9 

+  19.87 
20  32 
20  77 
21.21 

h    ni 
19  45.4 
19  44.5 
19  43.5 
19  42.5 

1st 

6th 

nth 

16th 

21st 

26th 

31st 

Day  of  the  Mon 

th     

2d 

7th 

12th 

17th 

22d 

27th 

Semidiameter 

Hor.  Parallax 

2:a 

4.0 

2:3 
4.1 

2:4 
4.2 

2:4 
4.2 

2:5 
4.3 

2:5 
4.4 

2:6 
4.5 

Semidiameter 

Hor.  Parallax 

5.1 

3:0 
5.2 

3.'l 
5.4 

3.'l 
5.5 

3!2 
5.6 

3:3 
5.8 

Note.— The  sign  +  indicates  north  declinations;  the  sign  —  indicates  south  declinations 


JUPITEK,  iai)4. 


GREENWICH    MEAN    TIME. 
NOVEMBER. 


Apparent 

Right 

Ascension. 


Noon. 


h    m       s 
6  26  17.67 
6  26    5.94 
6  23  43.34 
6  23  23.52 


Var.  of 
R.  A. 
fori 
Hour. 


-0.471 
0.50H 
0.810 
0.842 


Apparent 
Declination. 


+23  0  11.8 

23  0  24.0 

23  2  36.0 

23  2  52.8 


Var.  of 
Dec), 
fori 
Hour. 


Meridian 
Passage. 


+0.50  15  20.9 


0.52 
0.69 
0.71 


15  16.8 
14  39.0 
14  34.7 


SATURN,  mn. 


GREENWICH    MEAN    TIME. 
MARCH. 


"^K^t"'    I^r'a^^I    Apparent 
Asc'l'ifsfon.      ^lll^  I  Declfnation. 


h    m      s 
13  33  27.87 
13  33  15.58 
13  33    3.02 
13  32  50.18 


—0.506 
0.518 
0.529 
0.540 


Var.  of 
Decl. 
fori 
Hour. 


Meridian 
Passage. 


-6  50  20.2  +3.46  14  22.3 

6  48  56.4  3.52  14  18.2 

6  47  31.3  3.58|14  14.0 

6  46    4.9  3.63 14  9.9 


Day  of  tlie  Month 


Polar  Semidiameter., 
Horizontal  Parallax.. 


20.8 
2.0 


21.3 
2.0 


21.7 
2.0 


22.1 
2.1 


Day  of  the  Month 6th. 


Polar  Semidiameter. 
Horizontal  Parallax. 


8.8 
1.0 


1.0 


8.9 
1.0 


9.0 
1.0 


FIXED  STARS,  1894. 


MEAN   PLACES   FOR   THE    BEGINNING   OF   1894. 


Name  of  Star. 


Magni 
tude. 


Right  Ascension, 


Annual 
Variation. 


Annual 
Variation. 


a    Tsiuri  {Aldeha ran)    ... 

/3   Orionis  (Bigel) 

a    Orionis  (var.) 

a    Canis  Majoris  [Sirius) 
a    Canis  Min.  (Procyon) 

a    Leonis  (Regnlus) 

a^  Crucis 

a    Virginis  (Spica) 

a    Bootis  (Arcturus) 

/8'  Scorpii 

a    Lyrae  (  Vega) 

a    Aquilae  (Altair) 

/8  Aquarii 

a    Pis.  Aus.  {Fomalhai(t). . 


Note— The  sign  +  indicates  north  declinations;  the  sign  —  indicates  south  declinations 


h  m 

4  29 

5  9 

5  49 

6  40 

7  33 
10  2 

12  20 

13  19 

14  10 

15  59 

18  33 

19  45 

21  25 

22  51 


50.26 
26.60 
25.97 
28.63 
45.20 
43.63 
42.21 
36.48 
49.59 
16.40 
20.99 
36.70 
58.75 
47.58 


+  3.438 
+  2.882 
+  3.247 
+  2.644 
+  3.143 
+  3.200 
+  3.298 
+  3.154 
+  2.735 
+  3.481 
+  2.031 
+  2.928 
+  3.161 
+  3.324 


+  16  17  45.0 
-  8  19  28.0 
+  7  23  12.9 
-16  34  15.6 
+  5  29  46.7 
+  12  29  6.4 
-62  30  41.7 
-10  36  28.9 
+  19  44  3.6 
-19  30  54.4 
+  38  41  6.1 
+  8  35  18.5 
-62  14.8 
-30  11    2.3 


+  7.60 
+  4.38 
+  0.93 

-  4.73 

-  9.01 
-17.48 
-20.01 
-18.89 
-18.87 
-10.12 
+  3.18 
+  9.29 
+  15.68 
+  19.00 


THIS  BOOK  IS  DUE  ON  THE  LAST  DATE 
STAMPED  BELOW 

AN  INITIAL  FINE  OF  25  CENTS 

OVERDUE. 


LD  21-100?n-8,'34 


YD  n:^?4H 


